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To convert moles to molarity, divide the amount of solute in moles by the volume of the finished solution in litres. Molarity (symbol M, unit mol/L) is an amount concentration, so the same relationship also tells you how many moles a given volume of a known solution contains. This page gives the formula, a lookup grid for common mole and volume pairs, two worked examples and code you can paste into Excel, R or Python.
Mol to molarity formula
M = n / V, where n is the amount of substance in mol and V is the volume of the final solution in litres. Rearranged, n = M × V and V = n / M. If your volume is in millilitres, divide by 1000 first.
The mole is the SI unit of amount of substance: one mole contains exactly 6.022 140 76 × 1023 elementary entities, which fixes the Avogadro constant at exactly 6.022 140 76 × 1023 mol-1 (BIPM, The International System of Units, 9th edition, 2019; NIST, CODATA value of the Avogadro constant; both checked 2026-10-29). The SI brochure calls the derived quantity “amount-of-substance concentration”, which may simply be called “amount concentration”; clinical chemistry shortens it to “substance concentration”. Molarity is the everyday name for the same thing. For the difference between the two ideas, see moles vs molarity.
Mol to molarity table (moles and final volume)
Each cell is the molarity in mol/L for the moles of solute in the row dissolved to the final volume in the column. Every value was computed as moles divided by volume in litres. All entries in this grid are exact quotients, so no rounding was needed; a general result is best quoted to three significant figures.
| Moles of solute (mol) | 50 mL | 100 mL | 250 mL | 500 mL | 1 L |
|---|---|---|---|---|---|
| 0.001 | 0.02 | 0.01 | 0.004 | 0.002 | 0.001 |
| 0.005 | 0.1 | 0.05 | 0.02 | 0.01 | 0.005 |
| 0.01 | 0.2 | 0.1 | 0.04 | 0.02 | 0.01 |
| 0.025 | 0.5 | 0.25 | 0.1 | 0.05 | 0.025 |
| 0.05 | 1 | 0.5 | 0.2 | 0.1 | 0.05 |
| 0.1 | 2 | 1 | 0.4 | 0.2 | 0.1 |
| 0.25 | 5 | 2.5 | 1 | 0.5 | 0.25 |
| 0.5 | 10 | 5 | 2 | 1 | 0.5 |
| 1 | 20 | 10 | 4 | 2 | 1 |
To use it, find your moles in the left column and your final volume across the top. For a pair that is not listed, scale a listed row: doubling the moles at a fixed volume doubles the molarity, and doubling the volume at fixed moles halves it.
How to get moles from molarity and volume
Multiply the molarity by the volume in litres: n = M × V. The answer is in mol; multiply by 1000 for millimoles. To ask how much solution holds a target number of moles, use V = n / M. To go from moles to a mass of solid, multiply by the molar mass; the molarity and solution calculations guide works through that step, and NaOH molarity shows it for one reagent.
How to calculate moles from molarity and volume
Convert the volume to litres first, then multiply. A common slip is multiplying a molarity by a volume in millilitres, which gives a result 1000 times too large.
Worked examples
Example 1: moles and volume to molarity
A solution contains 0.050 mol of solute in a final volume of 250 mL. Convert the volume: 250 mL = 0.250 L. Then M = 0.050 mol / 0.250 L = 0.200 mol/L. This matches the 0.05 mol row and 250 mL column of the table.
Example 2: molarity and volume to moles
How many moles are in 500 mL of a 0.10 M solution? Convert: 500 mL = 0.500 L. Then n = 0.10 mol/L × 0.500 L = 0.050 mol, which is 50 mmol. Reading the table backwards confirms it: 0.05 mol in 500 mL gives 0.1 M.
Calculate it in Excel, R or Python
Excel (moles in A2, volume in mL in B2):
=A2/(B2/1000)For moles from molarity (molarity in A2, volume in mL in B2) use =A2*(B2/1000).
R
molarity <- function(mol, volume_ml) mol / (volume_ml / 1000)
moles <- function(molarity, volume_ml) molarity * (volume_ml / 1000)
molarity(0.050, 250) # 0.2
moles(0.10, 500) # 0.05Python
def molarity(mol, volume_ml):
return mol / (volume_ml / 1000)
def moles(molarity, volume_ml):
return molarity * (volume_ml / 1000)
print(molarity(0.050, 250)) # 0.2
print(moles(0.10, 500)) # 0.05Binary floating point cannot store most decimal fractions exactly, so a result such as 0.30000000000000004 can appear; round for display (for example round(x, 3)) rather than rounding intermediate values.
Final volume, not solvent volume
The V in the formula is the volume of the finished solution, not the volume of solvent you started with. Dissolving a solute usually changes the total volume slightly, so the usual approach is to dissolve it in less solvent and then make up to the mark of a volumetric flask. Method detail is in the buffer and solution preparation guide.
Write the unit of volume carefully. The SI brochure lists both l and L as symbols for the litre; the capital L was adopted in 1979 (16th CGPM) to avoid confusion with the numeral 1, which is why this page writes L.
Related conversions
- Concentrations written in millimolar or micromolar: millimolarity to molarity.
- Making a weaker solution from a stock: serial dilution calculations.
Safety: read the SDS before you weigh or dilute
Moles and molarity say nothing about hazard. Before preparing any solution, read the safety data sheet (SDS) for the specific chemical and follow your laboratory’s procedures; see how to read a safety data sheet.
Sources
- Bureau International des Poids et Mesures (BIPM), The International System of Units (SI Brochure), 9th edition, 2019: https://www.bipm.org/documents/20126/41483022/SI-Brochure-9.pdf (definition of the mole, amount concentration, litre symbols). Checked 2026-10-29.
- NIST, CODATA recommended value of the Avogadro constant: https://physics.nist.gov/cgi-bin/cuu/Value?na. Checked 2026-10-29.
FAQ
How do you convert moles to molarity?
Divide moles by the final solution volume in litres: M = n / V. For 0.25 mol in 500 mL, M = 0.25 / 0.500 = 0.5 mol/L.
How do you get moles from molarity?
Multiply molarity by volume in litres: n = M × V. A 2 M solution of 0.250 L holds 0.5 mol.
Does the volume mean the solvent or the whole solution?
The whole solution, after the solute is dissolved and the solution is made up to its final volume.
What is the difference between a mole and molarity?
A mole is an amount of substance; molarity is moles per litre of solution.
