Free tool

Burn-time calculator

Estimate how long until your skin is likely to burn at a given UV index. Same model as the Shade app.

Burn time by UV index and skin type

Bare skin, constant UV. Values are estimates in minutes; “4+ h” means no meaningful limit within four hours.

Skin type	UV 1	UV 2	UV 3	UV 4	UV 5	UV 6	UV 7	UV 8	UV 9	UV 10	UV 11	UV 12
I · Always burns	100 min	50 min	33 min	25 min	20 min	16 min	14 min	12 min	11 min	10 min	9 min	8 min
II · Burns easily	125 min	62 min	41 min	31 min	25 min	20 min	17 min	15 min	13 min	12 min	11 min	10 min
III · Sometimes burns	150 min	75 min	50 min	37 min	30 min	25 min	21 min	18 min	16 min	15 min	13 min	12 min
IV · Rarely burns	200 min	100 min	66 min	50 min	40 min	33 min	28 min	25 min	22 min	20 min	18 min	16 min
V · Very rarely burns	4+ h	125 min	83 min	62 min	50 min	41 min	35 min	31 min	27 min	25 min	22 min	20 min
VI · Never burns	4+ h	150 min	100 min	75 min	60 min	50 min	42 min	37 min	33 min	30 min	27 min	25 min

How the estimate is calculated

The UV index is a measure of skin-burning UV: each UV index point is about 1.5 J/m² of erythemally weighted UV per minute.
Each Fitzpatrick skin type has a typical minimal erythemal dose (MED), the dose that starts to redden skin: 200, 250, 300, 400, 500, 600 J/m² for types I to VI.
The estimate uses 75% of your MED as a margin below the burn threshold, and divides it by the dose per minute.
Sunscreen counts as ×5 and covering up as ×10 — far below the SPF number, because most people apply less sunscreen than labs do.

Sources: WHO — UV Index, Fitzpatrick T. B. (1988), Arch Dermatol 124(6).

Frequently asked questions

How long does it take to burn at UV 6?

With bare skin, roughly 16 min for skin type I, 20 min for type II and 25 min for type III, by this estimate. Reflection, altitude and your own skin shift the real answer.

Does SPF 30 mean I can stay out 30 times longer?

No. SPF is measured with a thick layer of sunscreen; most people apply a quarter to half of that and it wears off with sweat, water and time. This calculator counts sunscreen as a five-fold extension at most, and WHO advises reapplying every two hours.

Which skin type am I?

Type I always burns and never tans; II burns easily and tans a little; III sometimes burns and tans gradually; IV rarely burns and tans easily; V very rarely burns; VI is deeply pigmented and almost never burns.