Bikini Calculator — Sun Exposure & UV Safety Guide
Discover how long you can spend in the sun before risking sunburn — unprotected and with sunscreen — based on the UV index, your skin type and your SPF.
Skin type (Fitzpatrick scale)
Estimated time before sunburn for your skin type at this UV index
- 1
MED constant (your skin type)
200Minutes × UV-index product before sunburn occurs for this Fitzpatrick skin type. - 2
Unprotected burn time
200 ÷ 7 = 29
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Safe sun time (min) ≈ MED_constant / UV_index for your skin type, where MED_constant ranges from ~133 (Type I) to ~800 (Type VI). With sunscreen: multiply by SPF. Reapply every 2 hours. UV index 8+ is Very High — seek shade at peak hours (10 am – 4 pm).
Τύπος
How this is calculated
Sunburn occurs when your skin absorbs its Minimal Erythemal Dose (MED) — the threshold UV energy needed to redden the skin. The MED is fixed by your Fitzpatrick skin type (I through VI), ranging from roughly 200 J/m² for very fair skin (Type I) to 1200 J/m² for darkly pigmented skin (Type VI). UV intensity is measured by the UV Index, a linear scale where UV Index 1 corresponds to a UV dose rate of approximately 1.5 J/(m²·min) at the surface; at UV Index 7 that rate is 10.5 J/(m²·min). Dividing the MED by the current UV dose rate gives the unprotected burn time in minutes.
Sun Protection Factor (SPF) is the ratio of MED with sunscreen to MED without — SPF 30 allows skin to absorb 30 times its threshold dose before burning, so the burn time is multiplied by the SPF value. However, SPF ratings are measured in lab conditions with 2 mg/cm² of product; most people apply far less, effectively halving SPF performance. The reapplication reminder (maximum 2 hours, sooner if wet or sweaty) reflects that UV filters degrade and rub off over time.
These calculations are population-average estimates using typical mid-range MED values from WHO UV Index guidance. Individual variation is large: medications (tetracyclines, retinoids, diuretics), altitude, reflective surfaces (sand, water, snow) and cloud cover all alter actual exposure. Treat the output as a planning guide, not a clinical prescription.
Συχνές ερωτήσεις
The Fitzpatrick scale classifies skin into six types based on genetic pigmentation and tanning response: Type I (always burns, never tans) through Type VI (never burns, deeply pigmented). It was developed by dermatologist Thomas Fitzpatrick in 1975 and is widely used to assess UV sensitivity and sunscreen needs.
Mathematically, yes, but in practice the benefit plateaus. SPF 30 blocks about 97% of UVB; SPF 50 blocks about 98%. More importantly, most people under-apply sunscreen (using roughly half the test amount), and SPF degrades with sweat and water. Health authorities recommend reapplying at least every 2 hours regardless of SPF, and never relying on sunscreen as the sole UV defence.
The WHO rates UV index 6–7 as High, 8–10 as Very High, and 11+ as Extreme. At popular beach destinations in summer, UV index 9–11 is typical midday. At UV index 11 even an olive-skinned person (Type IV) without sunscreen can burn in about 40 minutes. Seek shade, wear protective clothing and apply broad-spectrum sunscreen.
Γνωστό και ως
TG we-Calculate Editorial Team. (2026). Bikini Calculator — Sun Exposure & UV Safety Guide [Online calculator]. TG we-Calculate. https://we-calculate.com/el/calculator/bikini-calculator
TG we-Calculate Editorial Team. "Bikini Calculator — Sun Exposure & UV Safety Guide." TG we-Calculate. 2026. https://we-calculate.com/el/calculator/bikini-calculator.
TG we-Calculate Editorial Team, "Bikini Calculator — Sun Exposure & UV Safety Guide," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/el/calculator/bikini-calculator
@misc{wecalculate_bikini_calculator, title = {Bikini Calculator — Sun Exposure & UV Safety Guide}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/el/calculator/bikini-calculator}}, year = {2026}, note = {TG we-Calculate} }
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