Molarity & Dilution Calculator

Calculates how much reagent to weigh for a solution of a given molarity, and how much stock and solvent a dilution needs (C1V1 = C2V2). Use it to prepare reagents and buffers or to plan a serial dilution.

How to use

1. On "Molarity", leave empty the one box you want among mass, molar mass, volume and concentration, and fill in the others with their units.
2. On "Dilution", leave one of C1, V1, C2 and V2 empty to get it, with the amounts of stock and solvent to mix. The "Serial dilution table" plans repeated dilutions.
3. Use "Convert units" for mg/mL, % w/v, ppm and other units.
4. For a hydrate or an impure reagent, find the "Reagent to weigh" on "Hydrate & purity".

How it works

• mass = concentration × volume × molar mass (m = C × V × M). A dilution keeps the amount of solute, so C1 × V1 = C2 × V2.
• ppm and ppb are taken as mg/L and µg/L, which holds for dilute water solutions. % w/v is grams per 100 mL; % v/v needs the solute density.
• For a hydrate, waters × 18.015 is added to the anhydrous molar mass, and the mass is divided by the purity.

Questions and answers

How many grams of NaCl make 1 L of a 1 M solution?

1 mol/L × 1 L × 58.44 g/mol = 58.44 g. Dissolve it and make the volume up to 1 L.

How do I use C1V1 = C2V2?

For 100 mL of 1 mM from a 10 mM stock, V1 = 1 × 100 ÷ 10 = 10 mL. Add 90 mL of solvent to 10 mL of stock.

How do I convert molarity to percent concentration?

Molarity (mol/L) × molar mass = g/L, and g/L ÷ 10 = % w/v. "Convert units" shows all units at once when you enter the molar mass.

How do I plan a serial dilution?

Enter the starting concentration, fold per step, number of tubes and volume per tube. The table lists the solvent, transfer and concentration for each tube.