Molarity Calculator
Solve molarity, grams of solute, solution volume or molar mass, and plan dilutions with C1V1 = C2V2. Molar mass can be worked out from a formula such as NaCl.
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About this toolWhat is the Molarity Calculator?
This molarity calculator answers the everyday bench question: how many grams do I weigh out to make this solution? Choose which quantity to solve for (molarity, mass of solute, volume of solution or molar mass), fill in the other three, and the answer appears as you type, along with the number of moles and the concentration in grams per litre.
You do not need to look up the molar mass. Type a formula such as NaCl, CuSO4·5H2O or C6H12O6 and it is calculated from IUPAC standard atomic weights, using the same parser as the Molecular Weight Calculator. Units cover kg to µg, litres to microlitres and M to nM.
The Dilution tab solves C1V1 = C2V2 for whichever of the four is missing and turns the answer into a recipe: how much stock to measure, how much solvent to add, and the dilution factor.
- Solve for molarity, mass, volume or molar mass
- Molar mass from a chemical formula
- C1V1 = C2V2 dilution with a ready-to-use recipe
- Units from kg to µg, L to µL and M to nM
- Live results, copy and share; no data leaves your browser
How to use the Molarity Calculator
- On the Molarity tab, choose what to solve for: Molarity, Mass, Volume or Molar mass.
- Enter the other values and pick their units. For molar mass, either type it in g/mol or type a chemical formula and let the tool calculate it.
- Read the result, the moles of solute and the mass concentration in g/L, and check the working in the steps panel.
- For a dilution, open the Dilution tab, choose the unknown (usually V1, the stock volume), and enter the stock concentration, final concentration and final volume.
- Measure the stock volume shown, then make up to the final volume. Copy or share the result to keep it with your lab notes.
Worked examples
250 mL of 0.5 M sodium chloride
Input
Solve for mass; 0.5 M, 250 mL, formula NaCl
Output
7.305 g of NaCl (0.125 mol, 29.22 g/L)
0.5 mol/L × 0.25 L = 0.125 mol, and 0.125 × 58.44 g/mol = 7.305 g.
0.1 M sodium hydroxide
Input
Solve for mass; 0.1 M, 500 mL, formula NaOH
Output
1.99985 g of NaOH
NaOH is 39.997 g/mol. In practice NaOH pellets absorb water and CO2, so the solution is standardised by titration after it is made.
Diluting concentrated hydrochloric acid
Input
Dilution; C1 = 12 M, C2 = 1 M, V2 = 500 mL, solve for V1
Output
41.667 mL of stock, about 458.33 mL of water, 12× dilution
12 × V1 = 1 × 500, so V1 = 41.67 mL. Add the acid to most of the water, then make up to 500 mL.
Working out molar mass from a known solution
Input
Solve for molar mass; 2 M, 80 g, 1 L
Output
40 g/mol
80 g gives 2 mol in 1 L, so each mole weighs 40 g. That fits sodium hydroxide.
Background and insight
Molarity (symbol c or M) is the amount of solute in moles per litre of solution: c = n / V. Since moles are mass divided by molar mass (n = m / M), the full relation is c = m / (M × V), which rearranges to give any one of the four quantities from the other three. One mole is exactly 6.02214076 × 10²³ entities, the Avogadro constant fixed in the 2019 SI redefinition.
The volume in molarity is the volume of the finished solution, not the volume of solvent added. Dissolving a solid changes the volume, which is why solutions are made up to the mark in a volumetric flask. Molarity also changes slightly with temperature because liquids expand; molality (moles per kilogram of solvent) does not, which is why it is preferred for colligative property work.
Dilution conserves the amount of solute: the moles in the aliquot of stock equal the moles in the diluted solution, so C1 × V1 = C2 × V2. The units only need to match on each side, so you can use mM and mL as long as both concentrations share a unit and both volumes share a unit. A dilution can only lower the concentration, so the calculator rejects a final concentration above the stock.
Common use cases
Making buffers and reagents
Get the mass to weigh for a stock solution of a given concentration and volume.
Serial dilutions
Plan each step of a dilution series for standards, cell culture or calibration curves.
Chemistry coursework
Check molarity, moles and dilution answers, and copy the formula steps.
Converting units
Move between M, mM, µM and nM, or between g/L and mol/L, without slipping a factor of 1000.
Tips and limitations
- For hydrated salts, use the hydrate formula (CuSO4·5H2O, 249.68 g/mol) if that is what is in the bottle, not the anhydrous one.
- Molarity is per litre of final solution. Dissolve the solute in less solvent first, then make up to volume.
- Volumes of different liquids do not add exactly; mixing acid or ethanol with water shrinks the total, so fill to the mark rather than adding a calculated solvent volume.
- Always add concentrated acid to water, never water to acid.
- For percent solutions (w/v), 1% means 1 g per 100 mL, which is 10 g/L. Divide by molar mass to get molarity.
Frequently asked questions
How do you calculate molarity?
Divide moles of solute by litres of solution. If you start from grams, first divide by molar mass: 7.305 g of NaCl is 0.125 mol, and in 0.25 L that is 0.5 M.
How many grams do I need for a 1 M solution?
One molar mass per litre. For 1 L of 1 M NaCl you need 58.44 g; for 100 mL you need 5.844 g. In general, grams = molarity × litres × molar mass.
What is the difference between molarity and molality?
Molarity is moles per litre of solution; molality is moles per kilogram of solvent. Molality does not change with temperature, while molarity changes slightly as the liquid expands.
How does C1V1 = C2V2 work?
The moles of solute stay the same when you dilute, so stock concentration times stock volume equals final concentration times final volume. Rearrange for the unknown, usually V1, the amount of stock to measure.
How do I convert mg/mL to molarity?
mg/mL is the same as g/L. Divide by the molar mass in g/mol to get mol/L. For example, 5.844 mg/mL of NaCl is 5.844 g/L ÷ 58.44 = 0.1 M.
What does mM or µM mean?
Millimolar (mM) is one thousandth of a mole per litre and micromolar (µM) is one millionth. 0.5 M is 500 mM or 500,000 µM.
Is there an in-depth guide to the Molarity Calculator?
Yes. “Molar Mass, Molarity, Dilutions and Half-Life: Lab Maths” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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