dilutioncalculator.co.uk§ Verified 20 Jun 2026 · Reviewed by A. Hargreaves, MChem (Hons)
v/v vs w/v vs w/w
Three percent notations, three different things. Confusing them is the most common dilution mistake on the lab bench and on the cleaner's trolley.
§ 1Definitions
- % v/v · ml of solute per 100 ml of total solution. Both volumes. 70 % v/v ethanol = 70 ml ethanol topped up to 100 ml.
- % w/v · g of solute per 100 ml of total solution. 0.9 % w/v NaCl = 9 g per litre.
- % w/w · g of solute per 100 g of total solution. 98 % w/w sulphuric acid is the lab concentrated grade.
IUPAC defines volume fraction φ separately from mass fraction w; the notations diverge as soon as densities differ from 1 g/ml.[6]
§ 2Conversion
- w/v → w/w divide by total solution density. 1 % w/v NaCl in water (density ≈ 1.005 g/ml) = 0.995 % w/w.
- w/v → v/v needs solute density. 1 % w/v glycerol = 1 g per 100 ml; glycerol density 1.26 g/ml; so 0.79 ml per 100 ml = 0.79 % v/v.
- % to mg/ml · multiply % w/v by 10. 0.9 % w/v = 9 mg/ml.
§ 3Which to use
- Liquid-in-liquid → v/v. Ethanol, methanol, surfactant dilutions.
- Solid-in-liquid → w/v. NaCl saline, agar, buffer salts.
- Concentrated reagent label → w/w. Acids, hydrogen peroxide, hypochlorite often quoted w/w on SDS.