Sunburn Time Calculator
Enter your skin type, today's UV index, and your sunscreen SPF to see how long you have before you burn — plus a shareable risk score for your beach day.
☀️ Your Sun Exposure
Summer Special⏱️ Your Burn Countdown
UV Risk: HighHigh UV Risk Today
With spf 30 and type iii skin, that's your estimated window before skin starts to burn.
🟢 0–2 Low 🟡 3–5 Moderate 🟠 6–7 High
🔴 8–10 Very High 🟣 11+ Extreme
How Sunburn Time Is Actually Estimated
Skin Type Sets Your Baseline
Dermatologists classify skin into six Fitzpatrick types, from Type I (pale, always burns) to Type VI (deep brown/black, almost never burns). Each type has a very different baseline tolerance to UV exposure before skin starts to redden.
UV Index Scales the Clock
The WHO/EPA UV Index measures how strong burning UV radiation is at a given place and time, from 0 (minimal) to 11+ (extreme). Burn time is roughly inversely proportional — a UV index of 10 burns skin about twice as fast as a UV index of 5.
SPF Numbers, Honestly Explained
By definition, SPF 30 extends burn time roughly 30x — but only when applied at the lab-tested amount (about a shot glass per body, a nickel-size dollop for the face) and reapplied every two hours or after swimming/sweating. Most people apply far less in practice, so treat this as a best-case ceiling.
A Worked Example
Say you're Fitzpatrick Type II (fair skin, burns easily) at the beach on a UV index 8 day. Bare skin, you'd start burning in roughly 19 minutes — barely enough time to set up an umbrella.
Apply SPF 30 correctly and that window stretches to around 9.5 hours in theory — but since most people under-apply and skip reapplication, a realistic plan is still to reapply every 2 hours, seek shade midday, and treat the calculator's number as a ceiling, not a guarantee.
Frequently Asked Questions
How is 'time until sunburn' calculated?
It starts from a widely used dermatological baseline for your Fitzpatrick skin type at UV Index 10, scales it inversely with today's actual UV index, then multiplies by your sunscreen's literal SPF factor (SPF 30 = 30x longer, by definition). It's an illustrative estimate, not personalized medical advice.
Why does skin type matter so much?
Melanin content varies widely by Fitzpatrick type and changes how much UV radiation your skin can absorb before burning. Type I skin can burn in under 15 minutes at high UV, while Type VI skin tolerates far longer exposure — though everyone's skin can still be damaged by UV over time.
Does SPF really extend my time that long?
Only in lab conditions, where testers apply about 2mg per square centimeter of skin — roughly a full shot glass for your body. Most people apply 25-50% of that amount and skip reapplication, so real-world protection is often lower. Reapply every 2 hours and after swimming or sweating.
Where do I find today's UV index?
Most phone weather apps show a daily UV index forecast, or you can check the EPA's UV Index tool at weather.gov. It changes throughout the day and peaks between 10am and 4pm.
💡 Explore Related Analytics Calculators
Lowering AmortizationCaffeine & Sleep Window
Model caffeine clearance half-life curves and find your safe bedtime.
Road Trip Costs
Forecast travel fuel, stays, meals, tolls, splits, and emissions.
Shark Attack Odds
Estimate your shark encounter odds from activity, time of day, and water clarity — plus a shareable Beach Boldness score.