Sun exposure estimator (vitamin D)
Estimate how much sun exposure you need to support vitamin D synthesis based on your skin type, the current UV index and the amount of exposed skin, along with the approximate threshold beyond which the risk of sunburn increases.
How it works
Skin synthesizes vitamin D when exposed to UVB rays. The amount produced depends mainly on three factors: UV intensity (UV index), the amount of melanin in the skin (skin type) and the area of exposed skin. This tool combines these three factors from a common reference (skin type III, 25% of skin exposed, UV index 6 ≈ 15 minutes for a useful dose) to estimate an indicative exposure time, as well as an approximate sunburn risk threshold beyond which protection is recommended.
Why does skin type change the results so much?
The more melanin the skin contains (skin types IV to VI), the more UVB it naturally filters: vitamin D synthesis is therefore slower and you need to stay in the sun longer to produce the same amount, but the sunburn threshold is also pushed back. Conversely, very fair skin (skin type I-II) synthesizes vitamin D faster, but also burns much more quickly.
What should I do if the UV index is low (winter, overcast sky)?
Below a UV index of about 3, skin synthesis of vitamin D becomes very limited regardless of exposure time, because UVB rays no longer pass through the atmosphere enough (the typical case in winter at temperate latitudes). In these conditions, dietary intake or supplements, on medical advice, are often needed to maintain a healthy level.
These estimates are indicative and simplified: they do not replace medical advice or a vitamin D blood test. Never stay in the sun beyond the sunburn risk threshold, and consult a healthcare professional with any questions about your vitamin D needs or sun exposure.
The calculation runs entirely in your browser: none of the data you enter is sent to a server.