Solution Preparation Calculator
Grams for % (w/v), molar & ppm solutions
Solute to weigh
9g
Dissolve the solute, then make up to the final volume (don't add solvent to a fixed volume).
ƒ Mass = concentration × volume (mode-dependent)
This calculator tells you how many grams of solute to weigh for a solution of a given concentration and volume — in % (w/v), molar (mol/L) or ppm. Choose the mode, enter the target concentration and final volume (and the molecular weight for molar solutions), and it returns the mass to weigh out.
% (w/v), molar and ppm
% (w/v) is grams per 100 mL — mass = (% ÷ 100) × volume in mL. Molar is mole-based — mass = molarity × molecular weight × volume in litres. ppm is parts per million — for dilute aqueous solutions, mass (g) = ppm × volume in litres ÷ 1000.
Worked example: 0.9% (w/v) saline in 1000 mL needs (0.9 ÷ 100) × 1000 = 9 g of NaCl.
Preparing the solution
Weigh the solute accurately, dissolve it in roughly 80% of the final volume, then make up to the final volume. For molar solutions you can get the molecular weight from the Molecular Weight Calculator.
Frequently asked questions
What does % (w/v) mean?
Percent weight/volume is grams of solute per 100 mL of solution. A 0.9% (w/v) saline solution contains 0.9 g of NaCl per 100 mL, i.e. 9 g per litre.
How do I prepare a ppm solution?
In dilute aqueous solution 1 ppm ≈ 1 mg/L. So a 50 ppm solution in 2 L needs 50 × 2 = 100 mg = 0.1 g of solute.
When do I need the molecular weight?
Only for molar solutions, where grams = molarity × molecular weight × volume in litres. The % (w/v) and ppm modes are mass-based and don't need it.
Should I add solvent to the solute or make up to volume?
Dissolve the solute in less than the final volume, then make up to the final volume in a volumetric flask. Adding solvent to a fixed mass gives the wrong concentration because the solute occupies volume.
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