Molarity, Dilution and ppm Calculator

How to use it

Choose What to calculate: molarity, a dilution, or percent and ppm.
For molarity, leave exactly one of the four fields empty: the tool works it out from the other three. For a dilution, leave one of C1, V1, C2 and V2 empty.
For percent and ppm, enter the Mass percent or the ppm, or the masses of solute and solution. The others follow.
Read the Result, and check each line of the Working. A dilution also shows the Water to add.

How molarity is calculated

Molarity is the amount of dissolved substance in moles per litre of solution. The amount in moles is the mass divided by the molar mass, so the molarity is the mass divided by the molar mass and by the volume in litres. The page takes the volume in millilitres and divides it by 1 000 first.

c = n ÷ V = (m ÷ M) ÷ V,   with V in litres

How dilution and percent are calculated

Adding solvent to a solution leaves the amount of solute unchanged, so C1 × V1 = C2 × V2. The concentration and volume units only have to match on the two sides. Mass percent is grams of solute per 100 g of solution, and ppm is milligrams per kilogram. One per cent is 10 000 ppm.

C1 × V1 = C2 × V2        mass percent = solute ÷ solution × 100        ppm = mass percent × 10 000

What the calculator does not cover

Temperature. Solutions change volume as they warm or cool, so a molarity given at one temperature is not exact at another. A mass percent does not change in this way.
Density for a concentrated or non-aqueous solution. The page takes a density of 1 g/mL for ppm, which holds for dilute aqueous solutions only.
Ions. A salt such as Na2SO4 gives two Na⁺ ions per formula unit, so the ion concentrations are not the same as the molarity of the salt.

Worked example: 250 mL of 0.50 M from a 2.0 M stock

The stock volume is V1 = C2 × V2 ÷ C1 = 0.50 × 250 ÷ 2.0 = 62.50 mL. The water to add is V2 − V1 = 250 − 62.50 = 187.5 mL, and the dilution factor is C1 ÷ C2 = 4.000.

Quantity	Value
Stock volume V1	62.50 mL
Water to add	187.5 mL
Dilution factor C1 ÷ C2	4.000

Frequently asked questions

How do I make a solution of a given molarity?

Work out the mass: mass = molarity × molar mass × volume in litres. Dissolve that mass in part of the solvent, then make the solution up to the final volume in a volumetric flask. Leave the mass field empty to get it.

Why is the water to add V2 minus V1?

The stock contains all the solute and the diluted solution has the same amount of it. The rest of the final volume is solvent, so the water is the final volume minus the stock volume.

Why does the calculator reject a target higher than the stock?

C1 × V1 = C2 × V2 would need a stock volume larger than the final volume when C2 is greater than C1. A dilution only makes a solution weaker, so use a more concentrated stock.

Is 1 ppm the same as 1 mg per litre?

For a dilute aqueous solution, yes: the page takes its density as 1 g/mL, so 1 ppm is 1 mg per kilogram and also 1 mg per litre. For a dense or non-aqueous solution, check the density before you use the ppm figure.

Why does mass percent not change with temperature, but molarity does?

Molarity divides by the volume, and the volume of a solution depends on its temperature. Mass percent divides by masses, which do not change when the solution is warmed.

Does the calculator keep my numbers or send them anywhere?

No. The results are worked out in your browser, and nothing you type is stored or sent to our server.

Sources

Figures and text last checked on Tuesday, November 10, 2026.

Result

Working