Know when to come in
UV Hour reads the UV forecast where you are, applies your skin type, and estimates the minutes before your skin reddens. There is no risk-free tan — this tells you when to come in. Free, no account, no app required.
This is a weather-based estimate, not a personal safety limit. Skin damage builds up before any redness shows, and these times assume unprotected skin under a clear sky. Do not use them to extend your time in the sun — and do not rely on them at all for children, or if you have a history of skin cancer, a skin condition, or take photosensitising medication.
For the rest of today in Columbus
UV 2.3 right now (low) · peak UV 3.3 at 16:00 · type II has about 51 min of unprotected sun before the first redness at the peak
- 16:00 Peak UV hour
- 51 min Est. first redness at peak, type II
- Briefly Protection recommended (UV 3+, WHO)
- UV 2.3 Right now (low)
How long your skin has, at each UV level
Pick the UV index you are dealing with. Each page carries the estimated time to first redness for all six skin types at that level.
- UV 1 Low · type II: 2 h 47 before redness
- UV 2 Low · type II: 83 min before redness
- UV 3 Moderate · type II: 56 min before redness
- UV 4 Moderate · type II: 42 min before redness
- UV 5 Moderate · type II: 33 min before redness
- UV 6 High · type II: 28 min before redness
- UV 7 High · type II: 24 min before redness
- UV 8 Very high · type II: 21 min before redness
- UV 9 Very high · type II: 19 min before redness
- UV 10 Very high · type II: 17 min before redness
- UV 11 Extreme · type II: 15 min before redness
Start from your skin type instead
- Type I Always burns, never tans. At UV 8, about 17 min before redness.
- Type II Burns easily, tans minimally. At UV 8, about 21 min before redness.
- Type III Burns moderately, tans gradually. At UV 8, about 25 min before redness.
- Type IV Burns rarely, tans easily. At UV 8, about 33 min before redness.
- Type V Burns very rarely, tans very easily. At UV 8, about 42 min before redness.
- Type VI Almost never burns, always tans. At UV 8, about 50 min before redness.
The UV index in one table
| UV index | Band | Type II before redness | What it means |
|---|---|---|---|
| 0–2 | Low | 83 min | No protection needed for most people. Too weak to build a tan. |
| 3–5 | Moderate | 56 min | Seek shade near midday. Sunscreen for fair skin. |
| 6–7 | High | 28 min | Protection required. Fair skin burns in under 20 minutes. |
| 8–10 | Very high | 21 min | Extra protection. Avoid the sun between 11:00 and 15:00. |
| 11+ | Extreme | 15 min | Unprotected skin burns in minutes. Stay indoors around midday. |
The full UV index scale, level by level →
Where the sun is strongest right now
- London — UV 4.2Moderate · United Kingdom · peak at 13:00 tomorrow · type II: 40 min to first redness at the peak
- Dublin — UV 3.8Moderate · Ireland · peak at 13:00 tomorrow · type II: 44 min to first redness at the peak
- Bristol — UV 3.6Moderate · United Kingdom · peak at 12:00 tomorrow · type II: 46 min to first redness at the peak
The rest of the calculator
- Tanning calculator Every UV level against every skin type, in one place.
- Sunburn calculator How many minutes before the first redness, for any combination.
- Best time of day to tan Why the answer is never "midday", and what it is today.
- What UV index is safe? Why no level is risk-free, and what changes between them.
- UV index scale 0 to 11+, what each band actually does to skin.
- Method & sources The three lines of arithmetic behind every number here.
Questions about the UV index
What is the UV index?
The UV index is a measure of the sunburn-causing radiation reaching the ground. One point equals 25 milliwatts per square metre of erythemally weighted irradiance. It runs from 0 to 11+, it peaks at solar noon, and it depends on the sun angle, the ozone layer, altitude and cloud — not on temperature. A cold clear day at altitude can carry more UV than a hot hazy one at sea level.
How long can I stay in the sun today?
It depends on the UV index and your Fitzpatrick skin type. At UV 8, type I reaches the first redness in about 17 min, type II in 21 min and type VI in 50 min. Those figures assume unprotected skin under a clear sky, and they mark where visible redness starts — not a target to reach. Damage accumulates well before them.
What UV index is safe to tan?
None, if the question is whether a tan can be risk-free. A tan is the skin's response to UV damage, so there is no level that removes the risk — the UV index only changes how fast it accumulates. The World Health Organization recommends sun protection from UV 3 upward. At UV 3, fair skin (type II) reaches the first redness in about 56 min; at UV 8 it is 21 min. UV Hour estimates that point and tells you when to come in. It does not certify any level as safe.
Is this medical advice?
No. UV Hour is arithmetic applied to a public weather forecast. It tells you when to come in, and it never recommends staying out past the erythemal threshold. It cannot account for medication, skin conditions, or how you actually react to the sun. If you have a history of skin cancer, take photosensitising medication, or have any doubt, ask a doctor.
Where does the data come from?
Clear-sky UV and cloud cover come from the MET Norway Locationforecast API, refreshed every 15 minutes and used under CC BY 4.0. Redness times come from the Fitzpatrick minimal erythemal doses published in the dermatological literature. That combination is a model, and a simple deterministic one: a fixed dose per skin type, a standard cloud attenuation curve, and corrections for altitude and ground reflection. The method page names every source and states what the model cannot know — how you applied sunscreen, what you take, and how your skin actually reacts.