Tools HubMoles & Molarity
Calculate molarity from moles and solution volume, or convert mass to moles with a supplied molar mass. View results in mol/L and mmol/L.
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Key Formula & Conditions
Learning modelMolarity is c = n / V, using amount n in moles and total solution volume V in litres. When starting from mass m and molar mass M, first calculate n = m / M.
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Result
Worked steps
Approximate results are displayed to at most 10 significant digits. Measurement significant figures and uncertainty are not inferred.
Formula and example
Molarity is c = n / V, using amount n in moles and total solution volume V in litres. When starting from mass m and molar mass M, first calculate n = m / M.
n = m / M; c = n / V
n = 0.025 mol, V = 250 mL = 0.25 L → c = 0.1 mol/L
- NaCl 5.844g / 500mL5.844 g ÷ 58.44 g/mol = 0.1000 mol → 0.2000 mol/L
- NaCl 1.461g / 250mL1.461 g ÷ 58.44 g/mol = 0.0250 mol → 0.1000 mol/L
- From 5 mmol / 100mL5 mmol = 0.005 mol ÷ 0.100 L → 0.050 mol/L
Common mistakes
- 250 mL is 0.25 L. Treating an mL value as litres causes a factor-of-1000 error.
- Use the total volume of solution after dissolving the solute, not the volume of solvent alone.
Check the assumptions
Use the total solution volume, not solvent volume. Volume depends on temperature. When starting from mass, supply the molar mass matching the compound and its hydration state.
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OpenStax · Chemistry 2e — Molarity ↗Done
Moles & Molarity
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Use worked examples within their stated inputs, units and assumptions. Tests cover specific cases at a specific time; they do not certify every input, expert review or standards compliance. Check the references and tool-specific verification notes, and enter your own access date when citing.
@misc{tools_hub_molar_concentration_2026,
author = {{Tools Hub}},
title = {Moles & Molarity},
year = {2026},
url = {https://the-tools-hub.net/en/tools/molar-concentration/},
note = {Accessed: YYYY-MM-DD}
}How to use
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Features
- Worked steps and unit conversions
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Use cases
Check your working
Compare formula substitutions and units with your own calculations.
Details
Use the total solution volume, not solvent volume. Volume depends on temperature. When starting from mass, supply the molar mass matching the compound and its hydration state.
Molarity, Dilution, Buffer Preparation, Beer-Lambert & pH
From molarity and stock dilution volumes (C₁V₁=C₂V₂) to Henderson-Hasselbalch buffer recipes, Beer-Lambert absorbance/calibration (A=εcℓ), and solution pH.
FAQ
How do mol/L and mmol/L relate?
1 mol/L equals 1000 mmol/L. Therefore 0.1 mol/L is 100 mmol/L.
Can I enter mass percent directly?
No. Mass fraction alone does not determine solution volume; you also need information such as density.
Are results exact?
Results use floating-point approximations, displayed to at most 10 significant digits. Measurement significant figures and uncertainty are not inferred.
Are inputs saved?
Inputs and results are not sent to a server or saved. They disappear when you leave the page.
Related guide
GuideBuffer 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.
GuideMolarity & 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.
GuideGuide to Osmotic Pressure & Van ’t Hoff’s Law: Formulas, Tonicity, and Molar Mass
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Related Tools
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Find the required stock volume from stock concentration, target concentration and final solution volume using C₁V₁ = C₂V₂.
Buffer Solution & Henderson-Hasselbalch Calculator
Calculate conjugate acid-base buffer recipes using the Henderson-Hasselbalch equation (pH = pKa + log([A⁻]/[HA])). Solves mass in grams for diverse hydrates, 1 M HCl/NaOH titration volumes, Good buffer temperature corrections (4°C, 25°C, 37°C), and Van Slyke buffer capacity β.
Beer-Lambert Law, Absorbance & Calibration Calculator
Solve the Beer-Lambert Law (A = εcℓ) for absorbance, molar concentration, molar absorptivity, or path length. Includes dilution factor (DF) and mass concentration (mg/L) conversions, absorbance A ⇄ percent transmittance %T, and least-squares calibration curve fitting for unknown sample quantification.
Osmotic Pressure & Van 't Hoff Calculator
Calculate osmotic pressure (kPa, atm, mmHg), molarity, temperature, and van 't Hoff factor i using Π = iCRT. Simulates physiological saline / glucose RBC tonicity (hemolysis vs. crenation) and macromolecular molar mass determination by membrane osmometry.
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