Tanning calculator

Very high UV

Find your row and your column. The number is how many minutes of unprotected sun it takes before the first redness appears — 0.667 × MED ÷ UV, the standard erythemal formula. At UV 8, that is 17 min for type I and 50 min for type VI.

Today in Columbus

UV 0.1 right now (low) · peak UV 8.6 at 14:00 · skin type II window 11:07–11:35 and 16:36–17:49

Very high UV

14:00 Peak UV hour
19 min Time to redness at peak, type II
11:07–11:35 First of 2 windows
11:20–17:13 Protection recommended (UV 3+, WHO)

Your window Under 40 min to redness UV index

Today's window in Columbus, by skin type. Times are local.
Skin type	Window	Time to redness at peak UV 8.6
I	17:03–17:49	16 min
II	11:07–11:35, 16:36–17:49	19 min
III	11:07–11:45, 16:13–17:49	23 min
IV	11:07–12:20, 15:21–17:49	31 min
V	11:07–13:34, 14:14–17:49	39 min
VI	11:07–17:49	47 min

Every UV level against every skin type

Minutes of unprotected sun before the first redness. Green rows are the levels where that skin type keeps a continuous window all day; red cells are under 20 minutes.
UV	Type I	Type II	Type III	Type IV	Type V	Type VI
UV 1	2 h 13	2 h 47	3 h 20	4 h 27	5 h 33	6 h 40
UV 2	67 min	83 min	1 h 40	2 h 13	2 h 47	3 h 20
UV 3	44 min	56 min	67 min	89 min	1 h 51	2 h 13
UV 4	33 min	42 min	50 min	67 min	83 min	1 h 40
UV 5	27 min	33 min	40 min	53 min	67 min	80 min
UV 6	22 min	28 min	33 min	44 min	56 min	67 min
UV 7	19 min	24 min	29 min	38 min	48 min	57 min
UV 8	17 min	21 min	25 min	33 min	42 min	50 min
UV 9	15 min	19 min	22 min	30 min	37 min	44 min
UV 10	13 min	17 min	20 min	27 min	33 min	40 min
UV 11	12 min	15 min	18 min	24 min	30 min	36 min

With sunscreen

SPF multiplies the time above by its factor — in laboratory conditions. The pages below carry the honest version, including what happens at the amount people actually apply.

Every UV level

Every skin type

Where the sun is strongest right now

Brighton — UV 6.5High · United Kingdom · peak at 13:00 · type II window 10:00–10:22
Bristol — UV 6.3High · United Kingdom · peak at 13:00 · type II window 11:17–12:12
Cardiff — UV 5.8High · United Kingdom · peak at 13:00 · type II window 11:17–12:18

How the calculator works

How does this tanning calculator work?

It uses the standard erythemal formula: minutes before the first redness = 0.667 × MED ÷ UV index, where MED is the minimal erythemal dose of your skin type (200 J/m² for type I up to 600 J/m² for type VI). Sunscreen multiplies the result by its SPF factor. There is no model and no dataset — it is three lines of arithmetic on a public weather forecast.

What do I need to know to use it?

Two things: the UV index where you are, which the chart on this page reads from the forecast automatically, and your Fitzpatrick skin type, which you can identify from what happens after thirty minutes of strong unprotected sun. Everything else follows.

What counts as a safe tanning window?

A stretch of the day where the UV index is at least 2 — below that, skin produces no melanin at all — and no higher than the level that still leaves 40 minutes before the first redness for your skin type. On strong days that splits into a morning slot and an afternoon slot, with the middle unavailable.

Does the calculator account for cloud, altitude and reflection?

Yes. Cloud cover comes from the forecast and is applied with the standard attenuation curve — a fully overcast sky removes about 75% of the UV, a half-covered one only about 7%. Altitude adds 12% per 1,000 m. Dry sand adds about 15%, water about 20%, fresh snow up to 80%.