Sun Safety Calculator

How long you can stay in the sun without burning depends on two things: how intense the UV radiation is (UV index) and how sensitive your skin is (Fitzpatrick skin type).

The UV Index is a dimensionless number, usually 0-11+, developed by the World Health Organization. UV 3-5 is moderate; 6-7 is high; 8-10 is very high; 11+ is extreme. In summer at midday in Australia or the American Southwest, UV 12-14 is not unusual.

Unprotected burn time is estimated from the Standard Erythema Dose (SED) — the minimum UV exposure that reddens skin. Each skin type has a different SED threshold.

Fitzpatrick Skin Types:

• Type I: Always burns, never tans. Very fair skin, often red hair and freckles.
• Type II: Burns easily, tans minimally. Fair skin, light eyes.
• Type III: Burns moderately, tans uniformly. Medium skin.
• Type IV: Burns minimally, tans easily. Olive skin.
• Type V: Rarely burns, tans darkly. Brown skin.
• Type VI: Never burns, deeply pigmented. Dark brown to black skin.

Approximate unprotected burn times (minutes): At UV 6: Type I = 10, Type II = 20, Type III = 30, Type IV = 50, Type V = 75, Type VI = 90+ These drop proportionally as UV rises.

SPF (Sun Protection Factor) multiplies your unprotected time — theoretically. SPF 30 means it should take 30 times as long to burn. In practice, most people apply far less sunscreen than tested, cutting real-world protection by 50-75%. SPF 30 well-applied still outperforms SPF 100 poorly applied.

This is an estimate. Actual burn times vary with altitude, reflective surfaces (snow, sand, water), and cloud cover. Consult a dermatologist for personal skin health guidance.