UV Exposure Calculator

How long until you burn? Enter today's UV Index and your skin type to get a sunburn-time estimate, WHO risk category and the SPF you actually need.

Estimate your safe sun time

Set the UV forecast for your hike and pick your Fitzpatrick skin type. Sunscreen SPF is optional — add it to see protected time.

UV Index From the weather app, e.g. 6–10 at high altitude / snow.

Fitzpatrick skin type How your skin normally reacts after unprotected sun.

Sunscreen SPF applied

Leave 0 for unprotected burn time. Real protection is re-applied every ~2 h.

Altitude boost Rough altitude UVI amplification.

Results

Burn time (unprotected)
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WHO UV category

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Recommended SPF

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Minimum daily choice

Protected time with your SPF

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Re-apply every 2 h

All skin types at this UV Index

Skin type	Burn time (unprotected)	Suggested SPF

How is this calculated?

Unprotected time-to-burn is set from the WHO UV Index erythemal reference. Base minutes at UVI 7 are used for each Fitzpatrick type (I≈10, II≈20, III≈30, IV≈50, V≈80, VI≈100 min) and scaled inversely with the adjusted UV Index: burn_min = base_min × 7 / adjusted_UVI. Adjusted UVI multiplies your input by the altitude factor (1.0 / 1.2 / 1.4). Effective protection from sunscreen multiplies burn time by the SPF number.未防护晒伤时间依据 WHO 紫外线指数 的红斑剂量参考设定。以 UVI=7 为基准，各 Fitzpatrick 肤型的基准分钟数为（I≈10、II≈20、III≈30、IV≈50、V≈80、VI≈100 分钟），再按调整后的紫外线指数反比缩放：晒伤分钟 = 基准分钟 × 7 / 调整后 UVI。调整后 UVI 按海拔系数（1.0 / 1.2 / 1.4）放大。防晒霜的实际保护时间则为晒伤分钟乘以 SPF 值。

adjusted_UVI = input_UVI × altitude_factor

Sources: WHO UV Index & Sun Protection guidance; Fitzpatrick skin typing; standard outdoor erythema-dose literature. Estimates only — snow, water and reflection add exposure.

Sun safety tip Above UVI 6, seek shade 10am–4pm, wear a hat and UPF clothing, and re-apply SPF 30+ every 2 hours or after sweat/water. Snow and water reflect up to 80% of UV.