Sunburn calculator
Time before the first redness = 0.667 × MED ÷ UV index. At UV 8 that is 17 min for skin type I and 50 min for type VI. Cloud, altitude and the surface under your feet all move that number — the tables below show by how much.
Tomorrow in Columbus
peak UV 6.6 at 13:00 · type II has about 25 min of unprotected sun before the first redness at the peak · protection recommended (WHO) 10:35–16:08
- 13:00 Peak UV hour tomorrow
- 25 min Est. first redness at peak, type II
- 10:35–16:08 Protection recommended (UV 3+, WHO)
| Skin type | At peak UV 6.6 |
|---|---|
| I | 20 min |
| II | 25 min |
| III | 30 min |
| IV | 40 min |
| V | 51 min |
| VI | 61 min |
Time to burn, every UV level against every skin type
| 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 |
The corrections most calculators skip
| Condition | Effect on UV | UV 8 becomes | Type II time |
|---|---|---|---|
| Clear sky, sea level, grass | reference | 8.0 | 21 min |
| Half cloud cover | −7% | 7.4 | 22 min |
| Fully overcast | −75% | 2 | 83 min |
| 2,000 m altitude | +24% | 9.9 | 17 min |
| Grass | +3% | 8.2 | 20 min |
| Beside water | +20% | 9.6 | 17 min |
| Dry sand | +15% | 9.2 | 18 min |
| Snow | +80% | 14.4 | 12 min |
These multiply. A clear day at 2,000 m on fresh snow turns UV 8 into about 17.9 — 9 min for type II. The full formula.
What this calculator will not do
It will not tell you how long to stay out. It tells you when to come in, which is a different number and the only one that is defensible: the erythemal threshold is a ceiling, and the damage curve does not start there — it starts below it and simply becomes visible there.
It also assumes a healthy adult with no photosensitising medication. Several common prescriptions — some antibiotics, retinoids, diuretics and anti-inflammatories among them — lower the erythemal threshold substantially, and no arithmetic on this page accounts for that.
Where the sun is strongest right now
- Darwin — UV 12.2Extreme · Australia · peak at 12:30 · type II: 14 min to first redness at the peak
- Cairns — UV 11.2Extreme · Australia · peak at 13:00 · type II: 15 min to first redness at the peak
- Brisbane — UV 8.4Very high · Australia · peak at 12:00 · type II: 20 min to first redness at the peak
Questions people ask about this
How do you calculate how long before sunburn?
Minutes before the first redness = 0.667 × MED ÷ UV index. MED is the minimal erythemal dose of your skin type, in joules per square metre: 200 for Fitzpatrick type I through to 600 for type VI. The 0.667 constant comes from the definition of the UV index itself — one point equals 25 mW/m², so one MED of 250 J/m² at UV 8 takes 1,250 seconds.
How long does it take to burn at UV 8?
About 17 min for type I, 21 min for type II, 25 min for type III, 33 min for type IV, 42 min for type V and 50 min for type VI — clear sky, sea level, no reflective surface.
Can you get sunburnt on a cloudy day?
Easily, and it is the most common way to be caught out. Cloud cuts UV far less than it cuts heat: half cover removes about 7%, and even full overcast leaves about 25% through. A UV 9 day under heavy cloud is still around UV 2.3, which burns type II in 72 min.
Does sand, water or snow make you burn faster?
Yes, and this is where most calculators stop. Reflected UV adds to what comes from the sky: about 15% from dry sand, 20% beside water, and up to 80% from fresh snow. At UV 6 on snow, the effective level is around 10.8 — a spring ski day carries more UV than a summer beach day.
What does the first redness actually mean?
One MED is the dose that produces a just-perceptible reddening 24 hours later. It is the threshold of visible damage, not a comfort limit — the biological damage begins below it. That is why UV Hour reports the time to reach it as a point to stay under, never as a target to reach, and why no UV level is presented as safe.