Molarity Calculator
Mass, moles, and volume in one step.
Molarity Calculator
Molarity (M) = mass ÷ molar mass ÷ volume in litres
Calculated instantly
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What This Calculator Does
The Molarity Calculator turns a weighed mass of solute and a final solution volume into molar concentration. It also reports the amount of substance in moles and millimoles, which is the bridge between a balance reading and the concentration written on a lab label.
How It Works
Dividing mass by molar mass gives moles. Dividing moles by the final volume in litres gives molarity, in moles per litre. Millimolarity is simply molarity multiplied by a thousand, which is why a 0.1 M solution is also 100 mM.
Example
Weigh 5.844 g of sodium chloride (58.44 g/mol) and make the solution up to 1,000 mL. That is 0.1 mol in 1 L, so the molarity is 0.100 M, or 100 mM. The same mass made up to 500 mL would be 0.200 M.
Formula
n = mass / molar massM = n / volume in litresM = mass / (molar mass × volume in litres)Volume must be in litres; divide millilitres by 1,000 first.
Reading the Results
Molarity
Moles of solute per litre of final solution. It is the concentration used in most stoichiometry and titration calculations.
Moles of solute
The amount of substance you actually weighed out. Moles are the counting unit that reaction equations are written in.
Sources and References
IUPAC — Compendium of Chemical Terminology (Gold Book)
Definitions of amount of substance and molar concentration
Molarity is defined as amount of substance divided by the volume of the solution.
NIST Chemistry WebBook (SRD 69)
Reference molar masses and thermodynamic data
A primary reference for the molar mass values used in stoichiometry.
References identify the method or data behind this calculator. Where a standard or tariff changes, the current edition applies, and the assumptions stated above take precedence over a remembered figure.
Frequently Asked Questions
Is molarity the same as molality?
No. Molarity is moles per litre of solution and changes with temperature. Molality is moles per kilogram of solvent and does not, which is why it is preferred for precise work near boiling or freezing points.
Do I use the volume of water or the final volume?
Always the final volume after the solute has dissolved and the flask has been made up to the mark. Adding 1 L of water to a solid usually produces slightly more than 1 L of solution.
How do I find the molar mass?
Add the standard atomic weights of every atom in the formula. Sodium chloride is 22.99 + 35.45 = 58.44 g/mol. The molecular weight calculator on this site does that arithmetic for any formula, including hydrates.
Why does the answer differ slightly from the label on the bottle?
Standard atomic weights are averages across natural isotope abundances, and assay purity is rarely exactly 100%. Both shift the effective molar mass, so volumetric standards are usually prepared with a correction factor.