Blog & Guides
Articles explaining how to use each tool, written for beginners and pros alike.
GuideHow to Calculate pH: From Hydrogen Ion Concentration and Back
Learn to calculate pH from hydrogen ion concentration with pH = −log₁₀[H⁺] and to reverse it with 10⁻ᵖᴴ — fully substituted examples, why one pH unit means ten times the concentration, and a free browser tool for checking.
GuideHow 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.
GuideMatrix 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.
GuideHow to Solve Quadratic Equations: The Formula and Discriminant
Learn to solve any quadratic equation by substituting into the quadratic formula, read the discriminant to predict the number of roots, and know when factoring is faster. Worked examples with full substitutions, common mistakes and a free calculator.
GuideHow 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.
GuideHow to Calculate Logarithms: Rules, Change of Base and Examples
Learn the one question behind every logarithm — what power of the base gives the argument? Work through log rules, the change-of-base formula and digit estimates with worked examples, then verify results with a free browser tool.
GuidePermutations vs Combinations: nPr and nCr Explained
Learn the one-question test that separates permutations from combinations, work through nPr and nCr examples, and check your answers with a free browser tool.
GuideArithmetic and Geometric Series: How to Find the Sum of a Sequence
Learn to find the n-th term and the sum of arithmetic and geometric sequences with step-by-step substitutions into Sₙ = n(a₁ + aₙ) ÷ 2 and Sₙ = a₁(1 − rⁿ) ÷ (1 − r). Includes the Gauss trick, the r = 1 caveat and worked examples.
GuideHow to Remember Trig Values: Deriving 30, 45 and 60 Degrees
Stop memorizing trig tables. Learn to derive every special-angle value of sin, cos and tan from two right triangles, convert degrees to radians, and read obtuse angles with quadrants and reference angles.
GuideHow 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.
GuideHow to Calculate Elapsed Time: Duration Formula Between Two Times
How to calculate elapsed time between a start and end time: subtracting in minutes, handling times that cross midnight, subtracting breaks, worked examples for work and study logs, and a free browser calculator that does it instantly.
GuideHow 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.
GuideHow 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.
GuideHow to Blur or Pixelate Images: Privacy Guide
Learn how to blur or pixelate images in your browser: what to hide, blur vs mosaic, strength guidelines, common mistakes, and a free tool.
GuideImage Cropping Guide: Ratios and Sizes Explained
Learn how to crop images in your browser: choose between 1:1, 16:9 and other ratios, find size guidelines for social media and forms, and keep quality intact.
GuideHow to Rotate & Flip Images Without Quality Loss
Learn how to rotate and flip images in your browser: why 90° turns never lose quality, why phone photos appear sideways, flip pitfalls and format tips.
GuideHow 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.
GuideHow to Choose a Color Scheme: The Basics
How to choose a color scheme: complementary, analogous, triadic and monochrome combinations, the 60-30-10 rule, and text contrast basics.
GuideHow to Check Contrast Ratio: WCAG Standards
How to check contrast ratio: relative luminance in WCAG 2.x, the AA and AAA thresholds (4.5:1, 3:1, 7:1), common color pair examples, and fixes.
GuideHow to Add and Subtract Fractions
Learn how to add and subtract fractions: finding common denominators, reducing answers, handling mixed numbers, and the mistakes to avoid.
GuideHow to Do Prime Factorization
Learn how to do prime factorization: what primes are, dividing by small primes step by step, factor trees, the divisor-count formula, and mistakes to avoid.
GuideMean, Median and Standard Deviation Guide
Learn how to find the mean, median and standard deviation: formulas with worked examples, when to use each measure, and how to read data spread.
GuideHow 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.
GuideHow to Read a QR Code from an Image or Screenshot for Free
How to read a QR code from an image or screenshot: camera vs browser methods, why codes fail to scan, and how to avoid QR phishing.
GuideHow 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.
GuideJapanese 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.
GuideHow Compound Interest Works: The Formula
How to calculate compound interest: formulas for a lump sum and monthly contributions, a worked example, and how rate and term change the outcome.
GuideHow 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.
GuideROT13 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.
GuideHow 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.
GuideHow Loan Payments Are Calculated: The Formula
How loan payments are calculated: the annuity formula behind monthly payments, how total interest works, and worked examples with a free calculator.
GuideHow 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.
GuideCompare 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.
GuideHow Many MB in a GB? Data Size Units Explained
How many MB in a GB? Learn what KB, MB, GB and TB mean, the 1024 vs 1000 difference, real-world size examples, and why USB drives show less.
GuideHow to Resize an Image: Sizes by Use Case
Learn how image resizing works, pixel size guidelines for websites, social media and forms, quality tips, and how to resize images free in your browser.
GuideRegex for Beginners: Common Patterns & a Free Tester
Learn regular expressions for beginners: what \d, \w, +, * and ? mean, practical email and phone patterns, flags, and testing with a free tool.
GuideRokuyo Explained: Taian, Butsumetsu & Lucky Days
Learn about Rokuyo - the six Japanese lucky days like Taian and Butsumetsu - how they are set by the lunar calendar, and how to check them for events.
GuideHow 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.
GuideHow to Calculate BMR & Daily Calorie Needs
Learn how to calculate BMR and daily calorie needs with the Mifflin-St Jeor equation, choose an activity level, and set intake targets for any goal.
GuideDouble 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.
GuideHow 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.
GuideWhat 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.
GuideTime Difference Guide: Japan & International Calls
Learn how time differences work, how daylight saving changes them, and schedule calls with Japan, New York and London using a world clock.
GuideURL Encoding Explained: Japanese URLs & Queries
Learn how URL encoding (percent-encoding) works, how to encode Japanese text, spaces and symbols, and build query parameters with a free tool.
GuideFull-width to Half-width: How to Convert Text
Learn the difference between full-width and half-width characters and how to convert text between them, including katakana and voiced marks.
GuideRoman 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.
GuideHow to Convert Number Bases: Binary and Hex
Learn how number base conversion works with clear steps and examples - converting between binary, octal, decimal and hexadecimal, plus a free conversion tool.
GuideHow 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.
GuideHow to Calculate Days Between Dates & Add Days
Learn how to calculate the days between two dates and find the date N days from today, including leap years and week/month conversions.
GuideHow to Calculate BMI and Healthy Weight
Learn how to calculate your BMI: the formula, Japanese classification (18.5/25), healthy weight, and the limits of BMI - with concrete examples.
GuideHow 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.
GuideBrowser 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.
GuideHow to Calculate Percentages and Ratios
Learn how to calculate percentages: X% of a total, X as a percentage of Y, and increase or decrease by X%. Practical examples for scores, growth and discounts.
GuideHow 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.
GuideHow to Count Characters: Full-Width vs Bytes
Learn how to count characters: full-width vs half-width, bytes vs characters, and how whitespace and line breaks are handled.
GuideHow to Convert Colors: HEX, RGB, HSL
Learn how to convert colors between HEX, RGB and HSL: reading color codes, conversion methods, and when to use each format.
GuideHow 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.
GuideHow to Convert Images: JPEG, PNG, WebP
Learn how to convert images: JPEG, PNG, WebP and HEIC differences, choosing the right format, and converting for free in your browser.
GuideHow to Format JSON: Pretty-Print and Validate
Learn how to format JSON: pretty-print vs minify, common syntax errors and fixes, and how to validate JSON with a free browser tool.
GuideHow 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.
GuideWhat 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.
GuideHow to Split a PDF: Extract Pages You Need
Learn how to split a PDF: extracting specific page ranges, splitting all pages, and pulling out only what you need - in your browser.
GuideHow 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.
GuideHow to Convert Unix Time to Dates
Learn how to convert Unix time (epoch timestamps) to dates: seconds vs milliseconds, timezones, and where developers use it.
GuideHow to Generate UUIDs: A Quick Guide
Learn how to generate UUIDs: what they are, how version 4 works, where to use them, and how to generate them in bulk in your browser.
GuideHow to Calculate Your Age Correctly
Learn how to calculate your exact age correctly, including how birthdays and February 29 (leap day) births are handled, with clear examples.
GuideWhat Is Base64? Encoding vs Encryption Explained
Learn how Base64 encoding works, where it is used, how it differs from encryption, and which data should never be treated as protected after encoding.
GuideHow to Convert CSV to JSON and Back
Learn how to convert between CSV and JSON as a beginner. Header rows, delimiters, Japanese data notes, and a free tool that handles it all in your browser.
GuideImage Compression Basics: Settings Explained
Learn how image compression works, the differences between JPEG, PNG and WebP, recommended settings by use case, and how to compress images for free.
GuideHow 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.
GuideHow to Merge PDFs: A Complete Guide
Learn how to merge PDFs as a beginner: reordering files, password-protected PDFs, file sizes, and a free browser-based tool that keeps documents private.
GuideHow to Create a QR Code: Free and Easy Methods
Learn how to create QR codes for free: step-by-step instructions for URLs and text, printing size and color guidelines, and commercial use rules.
GuideHow to Calculate Japanese Consumption Tax
Learn how to calculate Japanese consumption tax: tax-inclusive and tax-exclusive formulas, the reduced 8% rate for food, and rounding rules.
GuideHow to Convert Units: Length, Weight and More
Learn how to convert between centimeters and inches, kilograms and pounds, Celsius and Fahrenheit - with practical examples and tips for everyday use.