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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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
- From moles0.025 mol ÷ 0.25 L = 0.1 mol/L
- From mass1.461 g ÷ 58.44 g/mol = 0.025 mol → 0.1 mol/L
- From mmol5 mmol = 0.005 mol → 0.05 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 ↗How to use
- 1
Enter values and units
Use the example or enter your own conditions.
- 2
Calculate
Check the result and each calculation step.
- 3
Check assumptions
Review applicability and display precision, then copy inputs and results if needed.
Features
- Worked steps and unit conversions
- No account; calculation stays in your browser
- Copy inputs and results together
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.
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.
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