Percent solution calculator (w/v)
A percentage and a volume in; grams on the balance out.
Free, no account needed. Nothing you type is sent anywhere or stored — the arithmetic runs in your browser.
Inputs
Results
Weigh out
4g
- Same in milligrams
- 4000mg
What w/v actually means
Grams per 100 mL of final solution — not per 100 g, and not per 100 mL of solvent. So 4% paraformaldehyde is 4 g made up to 100 mL, and a 10% solution at 250 mL needs 25 g.
It is a convention rather than a real ratio: you are dividing a mass by a volume and calling the answer a percentage, which only works because a millilitre of water happens to weigh about a gram.
w/v, w/w and v/v are three different things
w/v is grams per 100 mL, which is this calculator. w/w is grams per 100 g of the finished mixture — used where density would otherwise mislead. v/v is millilitres per 100 mL, which is how ethanol and glycerol are usually quoted.
A protocol that just says “10% glycerol” almost always means v/v, and one that says “4% PFA” means w/v. When a recipe is ambiguous and the substance is a liquid, it is worth asking rather than guessing — the two differ by the density.
Make up to the mark
As with any solution: dissolve in less than the final volume, then bring it up. Adding 100 mL of water to 4 g of powder gives you rather more than 100 mL of 4% solution.