UV index & reapply timer
Today's UV where you are, and when to put more on
- Free, no sign-up
- Runs in your browser
Where are you?
Coordinates are sent to Open-Meteo for the forecast and nowhere else. Prefer not to share them? Search for a place by name instead.
Allow location, or search for a place, to see today's UV.
Nothing is shared until you choose one of the two.
What people use this for
- You do not know when to reapply. "Every two hours" ignores that UV at nine in the morning and one in the afternoon are not the same problem.
- You live somewhere with real seasons. In Norway the UV index swings from near zero in January to genuinely high in June. One habit cannot cover both.
- You are not sure you use enough. Most people apply between a quarter and a half of the tested amount, which is the single biggest gap between the number on the bottle and the protection you get.
Where the numbers come from
Today's UV forecast for your location comes from Open-Meteo, a free weather API that publishes hourly UV index values. Your coordinates are used to make that one request and are not stored — if you would rather not share location at all, you can search for a place by name instead.
The UV index itself is a standardised measure of erythemally weighted solar irradiance: it weights each wavelength by how effectively it causes skin reddening, so an index of 6 means roughly twice the burning potential of an index of 3. It is designed to be comparable between places and seasons, which is exactly what makes an hourly curve useful.
How the burn-time estimate works
Time-to-burn is estimated from the current UV index and the skin type you select, using the Fitzpatrick scale — a six-point classification based on how skin responds to sun exposure rather than on colour alone. Lower Fitzpatrick types reach a burning dose faster at the same UV index.
Treat the result as an order of magnitude, not a countdown. Individual variation is large, and the estimate does not know about altitude, snow or water reflecting UV back at you, cloud cover changing through the day, medication that increases photosensitivity, or how much sunscreen you actually applied. It is a way to see that midday in June is a different situation from four in the afternoon in September, not a licence to stay out until a timer runs down.
The reapplication schedule follows the same logic. Rather than a flat two hours, it clusters reminders around the peak of the day's curve, because that is when the dose you are accumulating is highest.
Quantity matters more than the number on the bottle
SPF is tested at 2 mg per square centimetre. For a face and neck that is roughly a third of a teaspoon, or the two-finger measure the tool shows at actual scale. Almost nobody applies that much, and the shortfall does not scale linearly: applying half the tested amount gives you considerably less than half the labelled protection.
The practical advice that follows is dull and effective — apply more than feels necessary, reapply after swimming or heavy sweating regardless of the schedule, and remember that shade and clothing do not need reapplying at all. On days when the index stays near zero, which in northern latitudes is most of the winter, none of this is urgent, and the tool will tell you so rather than nagging.
Frequently asked questions
Is my location stored?
Only on your own device. Your coordinates are sent to Open-Meteo to fetch the forecast and to nobody else, and a copy rounded to about a kilometre is kept in this browser's local storage so the page has an answer ready next time. There is no account and nothing is uploaded — 'Forget this location' deletes it. If you would rather not share location at all, search for a place by name instead.
How accurate is the time-to-burn?
It is an order of magnitude, not a countdown, which is why it is rounded to a coarse step rather than shown to the minute. It cannot know about altitude, snow or water reflecting UV back at you, cloud changing through the day, medication that increases photosensitivity, or how much sunscreen you actually applied.
Why not just reapply every two hours?
Because UV at nine in the morning and at one in the afternoon are not the same problem. Clustering reminders around the peak puts the protection where the dose actually is. The timer is there for the two-hour habit as well if you prefer it.
The index is zero. Do I still need sunscreen?
On a genuinely zero-index day the burning risk is negligible, which in northern latitudes covers much of the winter. The tool says so plainly rather than nagging. UVA still reaches you through cloud and glass, so daily use remains reasonable if pigmentation or ageing is your concern.
Why does the sunscreen illustration need calibrating?
Because a web page cannot find out how physically large your screen is — CSS millimetres are a polite fiction on nearly every display. Measuring against a bank card, which is 85.6 mm wide under ISO/IEC 7810 worldwide, is the only honest way to show two fingers of sunscreen at life size.
Will the reminder reach me if I close the tab?
No. It is an ordinary browser notification fired by this page, so the tab has to stay open. There is no background service and no push server behind it, which is also why it never needs an email address or an account.