Molarity is moles of solute per litre of solution (mol/L, written M). A 1 M solution contains one mole of solute in each litre.

How do I calculate molarity?

M = n / V, where n = mass / molar mass and V is volume in litres. For example 5.844 g of NaCl (molar mass 58.44 g/mol) in 1 L is 0.1 mol / 1 L = 0.1 M.

How much solute do I weigh for a target molarity?

mass = molarity × volume × molar mass. To make 2 L of 0.5 M NaCl you need 0.5 × 2 × 58.44 = 58.44 g.

Where do I find the molar mass?

Sum the atomic masses of every atom in the formula. NaCl is 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol; many periodic-table references list it directly.

Molarity Calculator

Molarity (M) is the concentration of a solution in moles of solute per litre of solution: M = n / V, where the number of moles n is the solute mass divided by its molar mass. This calculator works in three directions. Give it the mass, molar mass and volume to get the molarity; give it the target molarity, volume and molar mass to get the mass you need to weigh out; or give it the mass, molar mass and molarity to get the volume to dilute to. Mass accepts mg/g/kg, volume mL/L and concentration mM/M, and the result auto-scales to sensible units. The moles of solute are shown alongside every answer.

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Solve for

Molar mass (g/mol)Mass

Volume

Result

100 mM

Moles: 0.1 mol

Formula: M = (mass / molar mass) / volume

M = (mass / molar mass) / volume. Moles n = mass / molar mass. Concentration is moles of solute per litre of solution.

How to use

Pick what to solve for: molarity, mass, or volume.
Enter the molar mass of the solute (g/mol) and the two known quantities with their units.
Read the result and the number of moles involved.

Frequently asked questions

What is molarity?: Molarity is moles of solute per litre of solution (mol/L, written M). A 1 M solution contains one mole of solute in each litre.
How do I calculate molarity?: M = n / V, where n = mass / molar mass and V is volume in litres. For example 5.844 g of NaCl (molar mass 58.44 g/mol) in 1 L is 0.1 mol / 1 L = 0.1 M.
How much solute do I weigh for a target molarity?: mass = molarity × volume × molar mass. To make 2 L of 0.5 M NaCl you need 0.5 × 2 × 58.44 = 58.44 g.
Where do I find the molar mass?: Sum the atomic masses of every atom in the formula. NaCl is 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol; many periodic-table references list it directly.

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