Solution Preparation Calculator
How many grams of a compound to weigh out to make a solution of a given molarity and volume — the reverse of the molarity calculation.
What to weigh out for the molarity and volume you want.
How the solution preparation calculator works
Mass = molarity × volume in litres × molar mass. For 500 mL of 0.5 M NaCl: 0.5 × 0.5 × 58.44 = 14.61 g. Dissolve in a little less than the final volume, then make up to the mark.
If the reagent is a hydrate, use the hydrate's molar mass (CuSO4·5H2O is 249.68, not 159.61) or you will be short of copper. The purity row corrects for a reagent that is, say, 98% pure.
Formula: mass = M × V(L) × molar mass ÷ purity
Worked examples
| Inputs | Mass to weigh | Note |
|---|---|---|
| 500 mL of 0.5 M NaCl | 14.61 g | 14.61 g |
| 1 L of 0.1 M NaOH | 4 g | 4.00 g |
| 250 mL of 0.2 M CuSO4·5H2O | 12.484 g | use the hydrate's molar mass |
FAQFrequently asked questions
Should I dissolve in the full volume of water?
No — dissolve in less, then top up to the final volume in a volumetric flask. The solute displaces some water.
What about liquid reagents like concentrated HCl?
Use the dilution calculator with the stock's molarity (37% HCl is about 12 M) instead of weighing.
How accurate does the balance need to be?
To about 1% of the mass for routine work — 0.1 g on 14 g. Analytical standards need four-figure balances and dried reagents.
Why does purity matter?
A 98% reagent contains 2% something else, so you weigh 2% more to get the same amount of the compound. Enter it in Detailed mode.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.