Work out how much of a compound to weigh out for a solution of a given molar concentration and volume. Enter the molecular weight, the concentration you want and the final volume — the calculator returns the mass to weigh.
Mass = molecular weight × concentration × volume. Example shown: NaCl (MW 58.44) for 100 mL of 1 M.
The molarity formula
Molarity (M) is moles of solute per litre of solution. To prepare a solution:
mass = molecular weight × concentration (mol/L) × volume (L)
For example, to make 100 mL of 1 M NaCl (MW 58.44): 58.44 × 1 × 0.1 = 5.844 g.
How to use it
- Enter the molecular weight (g/mol) of your compound — it’s on the bottle or product page.
- Set the concentration you want (M, mM, µM or nM).
- Set the final volume. The mass to weigh out appears instantly, in convenient units.
Tips
- Dissolve in less than the final volume, then top up to the mark (q.s.) — don’t add solvent to a full volume.
- To dilute a stock instead of weighing from powder, use the dilution calculator (C1V1 = C2V2).
- For hydrated salts, use the MW of the hydrate form.
Frequently asked questions
How do I calculate how much to weigh for a molar solution?
Multiply molecular weight by the concentration in mol/L and by the volume in litres. Enter the three values above and the tool gives the mass.
What is molarity?
The number of moles of solute per litre of solution (mol/L), abbreviated M.
How do I make 1 L of 1 M solution?
Weigh out a mass in grams equal to the molecular weight, dissolve and top up to 1 L.
