Blog &amp; Guides

GCD and LCM: Methods, Word Problems and Three Numbers

Choose GCD or LCM for reduction, denominators, cuts and repeated cycles. Includes Euclidean steps, three-number pitfalls, offset starts, trillion-size input limits and exact large results.

How to Calculate Logarithms: Rules, Change of Base and Examples

Calculate logarithms from the definition, including bases below one. Worked change-of-base examples, log vs ln, domain checks, digit-count boundaries, rounded outputs, a diagram and FAQs.

Permutations vs Combinations: nPr and nCr Explained

Choose nPr or nCr by checking order, repetition and distinctness. Worked examples, a decision diagram, repeated digits, Lotto 6 odds, zero factorial and exact integer limits up to n=500.

How to Remember Trig Values: Deriving 30, 45 and 60 Degrees

Learn sin, cos and tan with two triangles and a unit circle. Exact-value tables, 150° and negative-angle signs, degree/radian inputs, undefined tan90° and practical checks.

Adding and Subtracting Fractions: Steps and Visual Checks

Compare fraction operations with tables and diagrams. Learn common denominators, negative mixed numbers, zero denominators, exact checks, seven-digit inputs and rounded decimal output.

How to Calculate Deviation Scores (T-Scores): Formula, Target Score & Percentiles

Calculate Japanese-style deviation scores T=50+10(x−μ)/σ and back-calculate target raw marks. Compare N vs. N−1 standard deviations, inspect a skewed-distribution counterexample where 50 is not the median, and check normal-model top percentile tables.

How to Use the Laws of Exponents: Product, Quotient, Power and More

Compare exponent laws, negative bases and reciprocals. Distinguish −2⁴ from (−2)⁴, understand the 0⁰ convention, fractional-exponent limits, scientific notation for 10⁻⁷ and exact versus approximate calculation.

Arithmetic and Geometric Series: How to Find the Sum of a Sequence

Compare arithmetic and geometric terms and sums with worked tables. Count terms correctly, handle r=1 and negative ratios, separate finite and infinite sums, and verify integer versus decimal calculator limits.

How to Do Prime Factorization

Factor 360 with a step diagram and comparison tables. Verify product and exponent forms, derive 24 positive divisors, choose GCD/LCM or fraction tools, and check the 15-digit input limit and recalculation workflow.

Mean, Median & Standard Deviation Guide: N vs. N−1, IQR, Outliers & Excel Comparison

Calculate mean, median, and standard deviation with a 5-score worked table. Compare population (N) vs. sample (N−1) divisors, interquartile range (IQR), CV, standard error, and Excel functions.

Matrix Determinant and Inverse: 2×2 and 3×3 Worked Examples

Learn to compute the determinant and inverse of 2×2 and 3×3 matrices with fully substituted examples. Covers the 2×2 inverse formula, cofactor expansion for 3×3, why det = 0 means no inverse, and the A × A⁻¹ = I check.

Updated: October 18, 2026Read article

How to Solve Quadratic Equations: The Formula and Discriminant

Learn to solve any quadratic equation by substituting into the quadratic formula, read the discriminant D = b² − 4ac with parabola comparison charts, and know when factoring is faster.

How to Find a Regression Line with Least Squares

Learn the least squares method step by step: build the sum table, compute Sxx and Sxy, find the slope a and intercept b, and read r and R² correctly. Includes worked examples, residuals, extrapolation and outlier cautions, and a free browser calculator for checking by hand.

How to Find the Dot Product of Two Vectors: Components and Angle

Learn the two formulas for the dot product — a·b = a₁b₁ + a₂b₂ and a·b = |a||b|cosθ — when to use each, how to find the angle between vectors, and what the sign tells you. Worked examples in 2D and 3D, plus a free browser tool.

Physics

Published: November 7, 2026Read article

Guide to Error Propagation: Formulas, Partial Derivatives, and Uncertainty Reporting

Master error propagation and uncertainty synthesis for science and engineering lab reports. Covers addition/subtraction, multiplication/division, power rules, general partial derivatives, root-sum-of-squares vs worst-case bounds, and GUM significant figure rounding with worked examples.

Simple Harmonic Motion & Pendulum Period: Equations, Experiments & Energy

Master simple harmonic motion: pendulum period T = 2π√(L/g), Borda’s finite amplitude correction, lab gravity inversion g = 4π²L/T², spring series and parallel stiffness, vertical equilibrium stretch, and phase relationships (90°/180°) with energy conservation.

How to Count Significant Figures and Apply the Rounding Rules

Count significant figures correctly, handle zeros, choose between half-up and half-even rounding, and apply the multiplication/division and addition/subtraction rules with worked examples.

Updated: October 18, 2026Read article

How to Use Ohm’s Law: Voltage, Current, Resistance and Power

Learn to use Ohm’s law V = IR to find voltage, current and resistance, plus the three power formulas P = VI, P = I²R and P = V²/R — with a 6-pair lookup table, comparison charts, and worked LED resistor examples.

Updated: October 17, 2026Read article

Thermal and Carnot Efficiency: Worked Examples and COP

Compare W/QH with 1−TC/TH using explicit inputs. Check Celsius-to-kelvin conversion, kW versus MW, matched-condition COP and calculator examples.

Published: October 15, 2026Read article

Bernoulli Equation: Velocity, Pressure, Flow and Limits

Reproduce pipe-flow, Venturi, Pitot and tank-drainage examples with stated inputs and units. Check pressure reference, the 183.16 kPa pipe result and the limits of the ideal-fluid model.

Published: October 14, 2026Read article

Circular Motion & Centripetal Force: Formulas, Centrifuge RCF, Bank Angles & Loops

Master uniform circular motion calculations: angular velocity ω, period T, rpm, speed v, centripetal acceleration a, and force F. Understand centripetal vs centrifugal force, laboratory centrifuge RCF (×g) conversion, highway bank angles, and vertical loop clearance physics.

RLC Circuit Impedance & Resonance: Series, Parallel, Phasors & Q Factor

Master RLC circuit analysis: impedance formulas Z = √(R² + (X_L - X_C)²), resonance frequency f₀ = 1/(2π√LC), series voltage magnification (V_L = V_C = Q×V), parallel antiresonance, phasor diagrams, power factor, and lab hand calculations.

Doppler Effect Calculations: Signs, Reflection and Conditions

Master the Doppler effect formula for moving sources and observers: how to choose plus and minus signs, sound speed adjustments for air temperature and wind, wall reflection echoes and beat frequencies, and reverse velocity calculations with worked physics examples.

How to Calculate Heat: Q = mcΔT, Thermal Equilibrium and Latent Heat

Learn when to use Q = mcΔT, Q = CΔT, energy conservation when mixing, or Q = mL for a phase change. Includes unit conversion (g and kg, J and cal, K and °C), mixing temperature examples, ice melting and water boiling calculations, common mistakes, and a free calculator for checking by hand.

Published: October 10, 2026Read article

Young’s Experiment and Diffraction Gratings: Worked Calculations

Master the physics of Young’s double-slit experiment (fringe spacing Δx = Lλ/d) and diffraction gratings (d sin θ = mλ). Step-by-step geometric and binomial derivations of optical path differences, bright/dark fringe conditions, glass slide shifts, liquid immersion effects, and maximum order limits.

Updated: October 10, 2026Read article

Thin-Lens Calculations: Signs, Magnification and Ray Diagrams

Master the thin lens formula (1/a + 1/b = 1/f) and magnification equation (m = -b/a) with intuitive sign conventions. Covers convex vs. concave lenses, focal length signs, real vs. virtual image decision tables, the three principal rays, magnifying glasses, and Bessel’s conjugate point method.

Updated: October 10, 2026Read article

Projectile Motion & Horizontal Launch: Formulas, Steps & Examples

Solve projectile motion and horizontal launches by separating horizontal constant-velocity motion from vertical constant-acceleration motion. Covers time of flight, peak height, range, elevated launches from cliffs, why 45 degrees maximizes range, and energy-conservation verification with worked examples.

Published: October 9, 2026Read article

Half-Life Calculation: Formula, Examples, and Common Mistakes

Calculate remaining amount, elapsed time and half-life with N = N₀(1/2)^(t/T). Worked examples with carbon-14 and cobalt-60, log₂ back-calculation, and common mistakes such as using e^(−t/T) or confusing half-life with mean life.

How to Find the Equivalent Resistance: Series and Parallel Circuits

Learn the two rules of equivalent resistance — series adds up (R = R₁ + R₂ + …) and parallel combines reciprocals (1/R = 1/R₁ + 1/R₂ + …) — with fully substituted examples, why parallel shrinks the total, and how to tackle mixed circuits.

Chemistry

Published: November 13, 2026Read article

science

Arrhenius Equation & Activation Energy Guide: 2-Temp Solving, Plots & Half-Lives

Master the Arrhenius equation k = A·exp(−Ea/RT): avoid kJ vs J and °C vs K traps, run multi-point OLS Arrhenius plots with Eyring parameters (ΔH‡, ΔS‡), compare CODATA vs textbook R, and solve 0th-, 1st-, and 2nd-order half-lives and shelf-life t90.

Published: November 10, 2026Read article

Guide to Faraday's Law of Electrolysis, Nernst Equation & Cell Potential: Formulas & Worked Examples

Master electrochemistry calculations from Faraday's law of electrolysis (Q = It, m = MIt/zF, STP gas volume) to the Nernst equation (E = E° − (RT/nF)ln Q), concentration cells, standard cell EMF E°cell, Gibbs free energy ΔG° = −nFE°, and equilibrium constant K with step-by-step worked examples.

Published: November 9, 2026Read article

Guide to Osmotic Pressure & Van ’t Hoff’s Law: Formulas, Tonicity, and Molar Mass

Master osmotic pressure calculations using van ’t Hoff’s law (Π = iCRT). Covers electrolyte dissociation factor i, physiological saline (0.90% NaCl) and glucose tonicity evaluation (RBC hemolysis vs. crenation), and polymer molar mass determination via membrane osmometry with worked examples.

Molarity & Dilution Calculation Guide: C=n/V, C₁V₁=C₂V₂, Mass % Conversion & Hydrates

Calculate molarity C=n/V and stock dilutions C₁V₁=C₂V₂ with step-by-step examples, convert mass percent and density via C=10ρw/M, and compare anhydrous vs. hydrate reagent masses.

How to Calculate pH: [H⁺], pOH, Weak-Acid 5% Rule & Ultra-Dilute Limits

Master pH and pOH calculations across all conditions: strong vs. weak acids (5% ionization rule vs. quadratic formula), water autoionization in 10⁻⁸ M ultra-dilute solutions, temperature-dependent pKw, and logarithmic significant figures.

How to Calculate Crystals Precipitated on Cooling

Find the mass of crystals that precipitate when a saturated solution is cooled: dissolved while hot, still soluble when cold, and the difference.

Published: October 20, 2026Read article

Buffer Solution Preparation & Henderson-Hasselbalch Guide: Hydrates, Titration & Temperature Shifts

Master conjugate acid-base buffer preparation using the Henderson-Hasselbalch equation (pH = pKa + log([A⁻]/[HA])). Step-by-step calculations for monobasic/dibasic sodium phosphate hydrate mass discrepancies, Tris base 1 M HCl titration volumes, 4°C cold-room pKa shifts (ΔpKa/ΔT), Van Slyke buffer capacity β, and acid-resistance simulations.

Published: October 18, 2026Read article

Beer-Lambert Law & Absorbance Calculations: %T, Dilution & Calibration Curves

Step-by-step guide to solving the Beer-Lambert Law (A = εcℓ) for absorbance, molar concentration, molar absorptivity, and path length. Covers μmol/L and 1 mm cuvette conversions, dilution factor (DF) and mg/L calculations, %T and dark-signal correction, linear calibration curves, and stray-light limits.

Ideal Gas Law vs Combined Gas Law: When to Use Each

Choose between PV = nRT and P₁V₁/T₁ = P₂V₂/T₂ by checking whether the amount of gas changes. Includes unit conversion (C to K, mL to L, mmHg to Pa), the 22.4 L molar volume at STP, gas density and molar mass, common mistakes, and a free calculator for checking answers.

How to Solve Redox Titration Calculations

Redox titrations balance electron moles, not H⁺ and OH⁻. Electron counts from half-reactions, worked examples for permanganate and iodometry, and common mistakes.

Published: October 6, 2026Read article

How to Calculate Mass Percent Concentration

Mass percent = solute mass ÷ solution mass × 100. Learn why 20 g of salt in 100 g of water is about 16.7% and not 20%, how to prepare 200 g of 8% brine, how mixing and evaporation change the concentration, and how to convert between mass percent and molarity, with a free calculator for checking.

Data Conversion & Generation

Binary, Decimal and Hex Conversion: Worked Examples and Signed Values

Convert 42 to binary 101010 and hex 2A, use a four-bit lookup table, and see when FF means 255 or −1. Check large integers and distinguish hex from UTF-8.

UUID v4 vs v7: How to Choose, Generate and Store UUIDs

Read the 36-character UUID layout, compare v4, v7 and v1, estimate collisions, and verify unique constraints. Try batch generation of up to 1,000 v4 IDs.

Data size calculation: image, audio, video and transfer time

Calculate uncompressed image, PCM audio and video sizes with worked examples, MB versus MiB tables and a 128-second transfer example. Check efficiency, compression and calculator assumptions.

GB to MB: decimal vs binary units, GiB and Mbps explained

Compare GB, GiB, MB and MiB with byte tables,32 GB and 512 GB examples, attachment limits and Mbps calculations. Follow the free converter without accidentally changing the input quantity.

URL Encoding Explained: Japanese URLs & Queries

Encode query values with examples for spaces, plus signs, punctuation and Unicode. Learn %20 versus +, double encoding, malformed escapes and why an entire URL needs different handling.

What Is Base64? Encoding vs Encryption Explained

Understand Base64 versus encryption with UTF-8, Base64url, padding and size examples. Follow text and file workflows, inspect invalid UTF-8 in Hex and download decoded bytes.

How to Format JSON: Pretty-Print and Validate

Format, minify and validate JSON with reproducible examples. Check large-integer rounding, duplicate keys, null, syntax errors and file downloads before replacing your original data.

Convert CSV and JSON: preserve IDs and check lost types

Reproduce CSV and JSON conversions with commas, quotes and leading-zero IDs. Compare null, missing fields, empty strings and nested data, then verify records before downloading.

How to Decode Hex to Text: UTF-8, Bytes and Common Errors

Decode hexadecimal bytes into UTF-8 text with Hello and Japanese examples. Learn why odd-length Hex and invalid UTF-8 fail.

Text Editing & Search

Regex for Beginners: Common Patterns & a Free Tester

Learn JavaScript regex with reproducible extraction and validation examples. Compare g/m/s/u flags, ASCII digits, slash-free pattern input, zero-width matches and the limits of format checks.

Full-width to Half-width: How to Convert Text

Compare exact fullwidth and halfwidth outputs, kana counts and UTF-8 bytes. Learn how width conversion differs from NFKC, when round trips lose information and how to prepare form fields.

Character count vs byte count: emoji, spaces and line breaks

Compare Unicode code points, UTF-16 units, grapheme clusters and UTF-8 bytes. Reproduce emoji and newline examples, understand the counter’s limits and check submission requirements.

Compare Two Texts and Find the Differences (Text Diff)

How to find the differences between two texts, line by line. Learn the basics of text diff, common use cases and pitfalls, plus a free browser-based diff tool.

Roman Numerals 1–100 Chart and 2026 Conversion

See every Roman numeral from 1 to 100, plus 2026 = MMXXVI. Learn subtractive notation, check a year chart, and convert integers from 1 to 3999 in your browser.

How to Change Text Case: Upper, Lower, Title

Uncapitalize text by converting it to lowercase. Compare lowercase, uppercase and title case with examples and a free browser converter.

How to Convert Numbers to Kanji

Learn how to convert Arabic numerals to kanji: basic rules, the man/oku/cho units, and tips for writing amounts in Japanese documents.

Ciphers, Hashes & Passwords

What Is SHA-256? How to Verify Files with a Hash

Learn what a hash is, how SHA-256 and MD5 differ, and how to verify a downloaded file against the official SHA-256 checksum using a free browser-based tool.

How to Create a Strong Password: Steps That Work

Learn how to create strong passwords: safe length and characters, the dangers of reusing passwords, and how to generate them for free.

ROT13 and Caesar Ciphers: How to Decode

Understand ROT13 with worked examples, compare shifts of 3 and 13, and see how case, punctuation and unknown shifts affect decoding.

How to Calculate and Decode XOR with a Known Key

Work through XOR bit rules and recover ABC using Hex key 01. Compare Hex and UTF-8 keys, understand repeating-key alignment and troubleshoot output.

Images, Design & QR

Choose a Color Palette: Complementary, Analogous and Triadic Workflows

Compare four palette schemes, actual generated color counts and HEX copying. Assign background, text and action roles, then check contrast on the finished screen.

WCAG 2.2 Contrast Ratios: Thresholds, Transparent Backgrounds and Checks

Choose the WCAG 2.2 threshold for text or UI, measure actual foreground and background colors, and avoid rounded-ratio and translucent-background mistakes.

HEX, RGB and HSL Conversion: Formats, Alpha and Rounding

Convert HEX, RGB and HSL with worked values. Check shorthand HEX, integer HSL rounding, alpha compositing and the tool’s supported input formats.

Updated: October 26, 2026Read article

Image Cropping Guide: Ratios and Sizes Explained

Separate crop aspect ratio from output pixels with a 640×400 example. Learn supported presets, keyboard movement, export formats and the crop-to-resize workflow without promising background removal or unchanged quality.

Updated: October 26, 2026Read article

How to Resize an Image: Sizes by Use Case

Choose pixel, percentage or longest-edge resizing with exact examples. Verify 640×400 to 320×200, preserve aspect ratio and distinguish pixels, encoded size and print dpi before submitting an image.

Updated: October 26, 2026Read article

How to Convert Images: JPEG, PNG, WebP

Compare JPEG, PNG and WebP for transparency, photos and diagrams. Follow the correct settings-before-file workflow, understand HEIC limits and inspect downloaded format, dimensions and byte size.

Make images smaller: choose dimensions, quality and file limits

Choose image compression settings from the actual upload limit and required dimensions. Compare JPEG, PNG and WebP, MB and MiB, portrait resizing, repeat processing and download checks.

Read QR Codes from Screenshots: Troubleshooting and Safety

Read a QR screenshot from the same phone or a PC. Check margins, blur, multiple codes, the 10 MiB file limit, and the decoded text before opening a URL.

How to Make a QR Code: Quiet Zones and Print Checks

Create a URL QR code and save a PNG. Learn the four-module quiet zone, print-size arithmetic, fixed M error correction, static-link limitations, and a practical pre-distribution check.

How to Create a Color Palette from an Image

Learn how to extract dominant colors from any photo or screenshot and turn them into a balanced color scheme, plus a free tool that runs entirely in your browser.

How to Combine Images: Merge Photos Side by Side or Stacked for Free

How to combine multiple images into one: horizontal and vertical layouts, adjustable gaps, PNG and JPEG output, tips for stitching screenshots and building before/after comparisons — with a free browser tool that needs no upload.

How to Blur or Pixelate Images: Privacy Guide

Compare blur and pixelation, why neither guarantees redaction, and when to crop or use opaque removal. Check the exported image before sharing it.

How to Rotate & Flip Images: Orientation and Export Quality

Learn how to rotate and flip images in your browser: how rotation differs from export quality, why phone photos appear sideways, flip pitfalls and format tips.

How to Make an Image Background Transparent (PNG)

Learn how to make an image background transparent and export a PNG: transparency basics, chroma keying vs AI cutouts, tolerance tips and common pitfalls.

PDF Editing

How to Split a PDF: Extract Pages You Need

Extract pages 2–4 from a five-page PDF with a concrete workflow. Check page positions versus printed labels, single-page extraction, noncontiguous selections, filenames and the limits of redaction or signature preservation.

How to Merge PDFs: A Complete Guide

Merge PDFs in the intended order using a two-page plus one-page example. Follow reorder and download steps, then check page content, forms, signatures, encryption and file-size limits.

How to Rotate a PDF and Save It

Why PDF pages open sideways, the difference between rotating the view and saving the rotation, and how to rotate and save a PDF in your browser.

Dates & Time

Rokuyo Explained: Japanese Lucky & Unlucky Days (Taian, Butsumetsu, Tomobiki) & Lunar Formula

Complete guide to Japan's six Rokuyo calendar labels (Sensho, Tomobiki, Senbu, Butsumetsu, Taian, Shakko). Learn their meanings, time-of-day rules, wedding and funeral customs, the (Lunar Month + Day) mod 6 formula, and 2026–2027 worked examples.

Unix Timestamp to Date: Seconds, Milliseconds, UTC and Local Time

Convert 10- and 13-digit timestamps, identify 12-digit and negative values, and check UTC, local time, reverse conversion and the signed 32-bit limit.

Updated: November 6, 2026Read article

Elapsed Time Calculator Guide: Overnight Hours, Breaks and Multi-Day Work

Calculate elapsed minutes, subtract overlapping breaks once, add hours to a time, and account for daylight saving changes with worked examples.

Updated: November 6, 2026Read article

Time Difference from Tokyo to New York and London: 2027 DST Dates

Calculate time differences from Tokyo using UTC, handle previous and next dates, and verify 2026 and 2027 DST transitions before scheduling a call.

Updated: November 6, 2026Read article

Days Between Dates: Add 30 or 90 Days and Count Both Ends

Calculate days between dates, 30 or 90 days later and inclusive counts. Compare leap years, month ends, and a Japanese public-holiday example.

Chronological and Counted Age: Dates and Japanese Rules

Compare chronological and Japanese counted age with reference dates, school-year boundaries, February 29 conventions and calculator scope.

Japanese Era to Gregorian: Reiwa, Heisei, Showa

How to convert Japanese era years (wareki) to Gregorian and back: the formula, charts for Reiwa, Heisei and Showa, and gannen notation.

How to Use a Timer and Stopwatch

Learn how to use a countdown timer and stopwatch: setting time, lap timing, and using them for the Pomodoro technique and time management.

Calculations & Units

Unit conversion guide: inches, pounds and temperature intervals

Convert inches to cm, pounds and ounces to grams, and Celsius, Fahrenheit and Kelvin. Tables and a decision diagram clarify screen diagonals, fluid ounces, temperature intervals and squared or cubed factors.

Percentage Calculations: Change, Reverse Percentages and Points

Choose percentage formulas by their baseline. Compare shares, changes, reverse discounts, percentage points and weighted rates, with a diagram, three calculator modes and rounding/copy cautions.

Compound Interest Formula & Savings Guide: Simple vs. Compound, EAR & Rule of 72

Calculate compound interest A=P(1+r/k)^(kn) and monthly savings with worked tables. Compare simple vs. annual vs. monthly compounding over 30 years, check 20-year monthly contribution matrices, verify the Rule of 72 against exact logarithms, and account for taxes and fees.

Loan Repayment Formula & Amortization Guide: Equal Payment vs. Equal Principal & Prepayment

Master the monthly loan payment formula, compare equal-payment and equal-principal amortization with 30M–50M rate tables, evaluate prepayment strategies, and check safe debt-to-income limits.

Published: October 6, 2026Read article

How to Calculate Electricity Costs: W, kW and kWh Explained

Electricity cost = power (kW) × time (h) × rate (per kWh). Learn the difference between W and kWh, how to work out monthly and yearly costs, where the 31 yen/kWh guideline comes from, why bills differ, and the cautions for air conditioners and refrigerators, with a free calculator for checking.

Updated: October 6, 2026Read article

How to Calculate Japanese Consumption Tax: Formulas, 8% & 10% Rates & Invoicing

Master Japanese consumption tax (JCT) calculations for standard 10% and reduced 8% rates. Learn why subtracting 10% is mathematically incorrect, invoice rounding regulations, and reference price tables.

How to Calculate Gas Cost: Distance and MPG

How to calculate gas cost: the distance ÷ efficiency × price formula, a comparison by efficiency, and how to measure real fuel economy from fill-ups.

How to Calculate Profit Margin and Markup

How to calculate profit margin from cost and selling price, the difference between margin and markup, and how to price from a target margin.

How to Find Area and Volume: Formulas

Area and volume formulas for squares, triangles, circles, cubes and spheres - with worked examples and a free browser calculator.

Double Discount Formula: Stacked Discounts with Examples

Calculate double discounts with a + b − ab/100. See why 30% off plus 10% off is 37%, and how reward points differ from checkout discounts.

How to Split a Bill & Calculate Per Person

Learn how to split a bill fairly: divide the total by the number of people, handle the remainder with rounding, and use a free calculator.

How to Calculate Percentages and Split Bills

Learn how to use a calculator: percentage calculations, splitting bills fairly, keyboard shortcuts, and a free browser-based calculator.

How to Calculate Discounts and Percent-Off

Learn how to calculate discounts: percent-off formulas, 10-50% off examples, tax-inclusive vs tax-exclusive, and rounding rules.

Notes

Browser Notepad: Auto-Save Notes Guide

Learn how to use an online browser notepad: auto-save, creating and searching notes, organizing tips, and device-only privacy.

Health Calculators

BMR & TDEE Calorie Calculation Guide: Mifflin–St Jeor Formula, Activity Multipliers & Age Table

Calculate resting energy expenditure (BMR/REE) and total daily energy expenditure (TDEE) with the Mifflin–St Jeor equation. Includes a 30-year-old, 175 cm, 70 kg worked example, 5 activity factors, age/sex reference tables, and why fixed calorie deficits have limits.

BMI Calculation Guide: Formula, Japanese vs CDC Categories & Reference Weight Table

Calculate Adult BMI (weight in kg / height in m²) with a 170 cm, 65 kg worked example. Compare Japan's 6-tier JASSO classification with WHO/CDC boundaries, check the 150–185 cm BMI-22 reference table, and review age-specific target BMI ranges.

Random Picks & Games

Updated: October 10, 2026Read article

How to Find Your Chinese Zodiac Sign: Year Chart and Calculator Guide

How to find your Chinese zodiac sign from a Gregorian year: the (year − 4) ÷ 12 formula, a chart from Rat to Boar with recent years, the Risshun caveat for January births, and zodiac basics for New Year cards — with a free browser finder.

How to Generate Random Numbers for Fair Draws

Generate random numbers for fair draws and raffles: no-duplicate picking, secure randomness vs pseudo-random, and test data generation.

What Is a Palindrome? Examples and How to Check

Learn what a palindrome is: famous Japanese and English examples, tips for creating your own, and how to check one instantly.