SunticHow to Read the UV Index
The UV index turns the invisible strength of the sun into a single number, but the number only helps if you know how to read it. The good news is that reading it is simple: you look at the value, find which risk band it falls into, and adjust your protection to match. Once you've done it a few times it becomes automatic, and it's a far better guide to sun risk than how warm or bright it feels outside.
What does the 0 to 11+ scale mean at a glance?
The World Health Organization groups the index into five risk bands. The higher the number, the faster unprotected skin can be damaged. Here is the full scale:
- 0-2 (Low): Minimal risk for the average person. Sunglasses on bright days are usually enough.
- 3-5 (Moderate): Moderate risk. Take care around midday with SPF, a hat and some shade.
- 6-7 (High): High risk. Protection is needed; cover up and seek shade in the middle of the day.
- 8-10 (Very high): Very high risk. Minimise midday sun; sunscreen, clothing and shade are essential.
- 11+ (Extreme): Extreme risk. Unprotected skin can burn very quickly, so take every precaution.
These bands are the same wherever you are in the world, which is what makes the index so useful. A reading of 7 means the same level of risk in London as it does in Sydney, even though the weather feels nothing alike.
How do you match your protection to the number?
Reading the index is really about turning the number into an action. The simplest rule of thumb is that once the index hits 3, it's worth protecting your skin. From there, the higher the value, the more layers of defence you stack up.
- At 0-2, no special measures are needed for most people in normal conditions.
- At 3-5, apply broad-spectrum SPF 30+, wear a hat and use shade around the middle of the day.
- At 6-7, add long sleeves or UV-protective clothing and limit time in direct sun from late morning to mid-afternoon.
- At 8-10, treat midday sun as something to avoid; reapply sunscreen often and stay in shade where you can.
- At 11+, cover as much skin as possible and stay out of direct sun during the peak hours.
What changes the reading through the day?
The UV index is not a fixed property of a place; it rises and falls constantly. The biggest driver is the position of the sun. UV peaks around solar noon, when the sun is highest, and is much weaker in the early morning and late afternoon. Season matters too, with summer values far higher than winter at the same latitude.
Conditions and surroundings change the reading as well. Cloud cover can lower UV, but thin or broken cloud lets most of it through, so a grey sky is not a guarantee of safety. Altitude pushes UV up because there is less atmosphere to absorb it, and reflective surfaces like snow, water and sand bounce extra UV onto your skin. This is why a reading taken a few hours ago, or for a city far away, can be misleading. To learn more about how each level feels in practice, see our guide to the UV index 1 to 11+ explained.
Where do you check it?
Because the index is so local and time-specific, the only reading that really matters is one for your exact spot right now. A weather app gives a rough sense of it, but a dedicated tool is faster and more precise. Suntic shows the live UV index for your location, along with a forecast so you can plan around the peak rather than getting caught out by it.
The most reliable habit is to make the reading effortless. A home-screen widget puts the current value in front of you without opening anything, so you can glance at it before you step outside. For a fuller introduction to what the number represents, our explainer on what the UV index is covers the basics.
Frequently asked questions
What does a UV index of 5 mean?
A UV index of 5 sits in the 'moderate' band. There is a real risk of damage around midday, so apply broad-spectrum SPF 30+, wear a hat and use shade during the strongest part of the day.
How do I check the UV index for my location?
Use a dedicated tool rather than guessing from the weather. The Suntic app reads the live UV index for your exact location and shows it on a widget.
Is the UV index the same all day?
No. It rises toward solar noon and falls in the afternoon, and it changes with cloud, season and altitude. That's why it's worth re-checking through the day rather than relying on a single morning reading.
