Work out uv exposure safe time instantly with clear inputs, formula shown and shareable results.
Converts the UV index into erythemal irradiance and divides the minimal erythema dose for your phototype by it to give the time to visible reddening.
UV dose and time
Erythemal irradiance (W/m2) = UV index x 0.025; time to one MED (s) = MED (J/m2) / irradiance; correctly applied sunscreen multiplies that time by its SPF
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
Only with the full 2 mg/cm2 test dose; real-world application typically achieves a third to a half of the labelled protection.
No. Snow, sand and water reflect ultraviolet and shorten the safe time considerably.