Work out sunscreen quantity instantly with clear inputs, formula shown and shareable results.
Applies the regulatory test dose of 2 mg per square centimetre to the exposed skin area, which is what the labelled SPF actually assumes.
Application quantity
Grams = exposed area (cm2) x 2 mg/cm2 / 1000; a full adult body of 1.8 m2 needs about 36 g, roughly seven teaspoons
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
Applying half the test dose gives far less than half the labelled protection, because SPF does not scale linearly with thickness.
Every two hours, and immediately after swimming, towel drying or heavy sweating.