What does the UV index measure?
The UV index describes the level of ultraviolet radiation. A higher number means greater potential for skin and eye damage. It is a public-health indicator, not a score for how suitable a day is for tanning. WHO explains how the scale works.
When you open a forecast, check whether the number describes this hour or the maximum expected today. Those answer different questions. A daily maximum can be useful for planning ahead, while an hourly view shows how conditions are expected to change.
How to read the scale
| UV index | What to take from it |
|---|---|
| 0–2 | The lower end of the scale. This is not a personalised exposure allowance. |
| 3–7 | Sun protection matters. Seek shade around midday and use clothing, a hat and sunscreen. |
| 8 and above | Extra care is needed. Avoid midday exposure and prioritise shade and protection. |
These bands summarise WHO guidance. Follow local advice and any individual advice from your clinician.
UV index and temperature answer different questions
Use temperature to decide what the weather may feel like, and UV to understand ultraviolet conditions. Keep the two readings separate when checking an outdoor forecast.
A useful check is to read the location first, the forecast time second, and the UV value third. This avoids comparing a current reading for one city with a daily maximum for another.
Does a UV number tell you how long to tan?
No. A UV forecast is not a personal countdown to skin damage. The NHS states that there is no safe or healthy way to get a tan. Sunscreen is not a reason to extend time in the sun.
An app can display a forecast or organise reminders. Neither a timer nor a skin-type setting makes UV exposure safe.
Check a forecast on your iPhone
Start with the Weather app if you only need a UV reading. Our iPhone UV index guide explains where to look.
If you also want session organisation, Tantastic combines hourly UV with guided timers and a private progress timeline. Compare that workflow with other options in our UV app shortlist.
Sources and further reading
Feature descriptions use the linked product information and this site’s Tantastic overview. Check the current listing and purchase screen before subscribing. Health information is general guidance, not individual medical advice.
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Hourly UV, guided timers and optional private progress photos on your iPhone.
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