Molarity Calculator
A free molarity calculator that finds the molar concentration (mol/L) from mass and molecular weight — or the mass you need to weigh out for a target molarity.
Enter the mass, molecular weight and volume to find molarity.
How to calculate molarity
Molarity (M) measures how much solute is dissolved in a solution, expressed in moles per litre. It is defined as the number of moles of solute (n) divided by the volume of solution in litres (V):
When you start from a mass rather than a mole count, first convert the mass to moles by dividing by the molecular weight (MW, in g/mol). That turns the definition into a single step: molarity = mass ÷ (molecular weight × volume). To go the other way and find the mass to weigh out, rearrange to mass = molarity × molecular weight × volume.
Worked example
Suppose you want to make a sodium chloride (NaCl) solution. NaCl has a molecular weight of 58.44 g/mol. If you dissolve 5.844 g of NaCl in enough water to make 1 L of solution, the molarity is 5.844 ÷ (58.44 × 1) = 0.1 M. Equivalently, to make 1 L of a 0.1 M NaCl solution you would weigh out 0.1 × 58.44 × 1 = 5.844 g.
Related tools
Need to dilute that stock to a lower concentration afterwards? Use the home dilution calculator. If your concentration is already in mg/mL, convert it with the mg/mL to molarity calculator.
Frequently asked questions
›What is molarity?
Molarity is the concentration of a solution expressed as the number of moles of solute per litre of solution, with units of mol/L (abbreviated M). A 1 M solution contains exactly one mole of dissolved substance in every litre. It is the most common way chemists describe how concentrated a solution is.
›How do you calculate molarity?
Divide the moles of solute by the volume of solution in litres: M = moles ÷ litres. If you only know the mass, first convert it to moles by dividing by the molecular weight (g/mol), which gives the combined formula M = mass ÷ (MW × volume). Enter your mass, molecular weight and volume above and the calculator does this for you.
›What is the difference between molarity and molality?
Molarity (M) is moles of solute per litre of total solution, so it depends on volume and changes slightly with temperature. Molality (m) is moles of solute per kilogram of solvent, which is mass-based and therefore temperature-independent. For dilute aqueous solutions near room temperature the two values are close, but they are not interchangeable.
›Is this molarity calculator free?
Yes. This molarity calculator is completely free, runs entirely in your browser, and needs no sign-up. Your numbers are never sent to a server.
Related calculators
Solve C₁V₁ = C₂V₂ for any unknown — stock concentration, volume, or final concentration.
Convert between moles, volume, and molar concentration (mol/L) in any direction.
Turn a 1:N ratio into exact stock + solvent volumes for any final amount.
Dilute a stock solution to a target concentration with full unit switching.
Convert mg/mL to molarity (and back) using molecular weight — both directions.
Parts per million ⇆ mg/L ⇆ percent, plus the mass of solute for a target ppm.