{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"uv-exposure-time"},"result":{"entity_type":"calculator","id":"uv-exposure-time","calculator_id":"uv-exposure-time","canonical_url":"https://tttkmbb.com/health/uv-exposure-time","name":"UV Exposure Time Calculator","title":"UV Exposure Time Calculator – Minutes to Sunburn by UV Index, Skin Type and SPF","category":"health","category_name":"Health","tool_name":"estimate_uv_burn_time","featured_mcp_tool":false,"description":"Estimates the time to skin reddening (erythema) from the UV index, the Fitzpatrick skin type (minimal erythema dose 200–1000 J/m²) and sunscreen SPF, and returns the WHO UV index category with its protection advice.","use_when":"You want a theoretical sunburn-time estimate for a UV index forecast and a skin type, with or without sunscreen, shade or cloud cover.","do_not_use_when":"You need a safety guarantee: individual MED varies about two-fold within a skin type, sunscreen is usually under-applied, and snow, sand and water reflection add exposure; the result is informational only, not medical advice.","inputs":[{"name":"uv_index","label":"UV index","type":"number","required":true,"max":16,"exclusive_min":0,"description":"Forecast or measured UV index (1 unit = 25 mW/m² of erythemally weighted irradiance).","example":8},{"name":"skin_type","label":"Fitzpatrick skin type","type":"enum","required":true,"values":[{"value":"type_1","label":"I – very fair, always burns, never tans (MED 200 J/m²)","aliases":["1","i"]},{"value":"type_2","label":"II – fair, burns easily, tans minimally (MED 250 J/m²)","aliases":["2","ii"]},{"value":"type_3","label":"III – medium, sometimes burns, tans gradually (MED 300 J/m²)","aliases":["3","iii"]},{"value":"type_4","label":"IV – olive, rarely burns, tans easily (MED 450 J/m²)","aliases":["4","iv"]},{"value":"type_5","label":"V – brown, very rarely burns (MED 600 J/m²)","aliases":["5","v"]},{"value":"type_6","label":"VI – dark brown or black, never burns (MED 1000 J/m²)","aliases":["6","vi"]}],"description":"Fitzpatrick sun-reactive skin type; sets the minimal erythema dose (MED) used for the estimate.","example":"type_2"},{"name":"spf","label":"Sunscreen SPF","type":"number","required":false,"default":1,"min":1,"max":100,"description":"Sun protection factor of the sunscreen applied (1 = no sunscreen). Used as a theoretical multiplier of the burn time.","example":30},{"name":"shade_factor_percent","label":"Shade / cloud reduction","type":"number","unit":"%","required":false,"default":0,"min":0,"max":90,"description":"Percentage of UV blocked by shade, clouds or clothing (open shade ≈ 50 %, heavy overcast ≈ 70 %).","example":0}],"outputs":[{"name":"minutes_to_burn_unprotected","label":"Minutes to burn without sunscreen","type":"number","unit":"min","decimals":1,"description":"MED / dose rate, with the shade factor applied but no sunscreen."},{"name":"minutes_to_burn_with_spf","label":"Minutes to burn with SPF","type":"number","unit":"min","decimals":1,"description":"Unprotected time × SPF (theoretical, full-label protection)."},{"name":"hours_with_spf","label":"Hours with SPF","type":"number","unit":"h","decimals":2,"description":"minutes_to_burn_with_spf / 60."},{"name":"med_j_m2","label":"Minimal erythema dose","type":"number","unit":"J/m²","decimals":0,"description":"Erythemally weighted UV dose that produces just-visible reddening for the chosen skin type."},{"name":"uv_dose_rate_j_m2_per_min","label":"UV dose rate","type":"number","unit":"J/m²/min","decimals":2,"description":"uv_index × 1.5 J/m² per minute, reduced by the shade factor."},{"name":"uv_index_category","label":"UV index category","type":"string","decimals":4,"description":"WHO exposure category: low 0–2, moderate 3–5, high 6–7, very high 8–10, extreme 11+ (index rounded to the nearest whole number)."},{"name":"advice","label":"Protection advice","type":"string","decimals":4,"description":"WHO sun-protection message for the category."}],"input_schema":{"type":"object","properties":{"uv_index":{"description":"Forecast or measured UV index (1 unit = 25 mW/m² of erythemally weighted irradiance).","type":"number","maximum":16,"exclusiveMinimum":0,"examples":[8]},"skin_type":{"description":"Fitzpatrick sun-reactive skin type; sets the minimal erythema dose (MED) used for the estimate.","type":"string","enum":["type_1","type_2","type_3","type_4","type_5","type_6"],"examples":["type_2"]},"spf":{"description":"Sun protection factor of the sunscreen applied (1 = no sunscreen). Used as a theoretical multiplier of the burn time.","type":"number","minimum":1,"maximum":100,"default":1,"examples":[30]},"shade_factor_percent":{"description":"Percentage of UV blocked by shade, clouds or clothing (open shade ≈ 50 %, heavy overcast ≈ 70 %). Unit: %.","type":"number","minimum":0,"maximum":90,"default":0,"examples":[0],"x-unit":"%"}},"additionalProperties":false,"required":["uv_index","skin_type"]},"output_schema":{"type":"object","properties":{"minutes_to_burn_unprotected":{"description":"MED / dose rate, with the shade factor applied but no sunscreen. Unit: min.","type":"number","x-unit":"min"},"minutes_to_burn_with_spf":{"description":"Unprotected time × SPF (theoretical, full-label protection). Unit: min.","type":"number","x-unit":"min"},"hours_with_spf":{"description":"minutes_to_burn_with_spf / 60. Unit: h.","type":"number","x-unit":"h"},"med_j_m2":{"description":"Erythemally weighted UV dose that produces just-visible reddening for the chosen skin type. Unit: J/m².","type":"number","x-unit":"J/m²"},"uv_dose_rate_j_m2_per_min":{"description":"uv_index × 1.5 J/m² per minute, reduced by the shade factor. Unit: J/m²/min.","type":"number","x-unit":"J/m²/min"},"uv_index_category":{"description":"WHO exposure category: low 0–2, moderate 3–5, high 6–7, very high 8–10, extreme 11+ (index rounded to the nearest whole number).","type":"string"},"advice":{"description":"WHO sun-protection message for the category.","type":"string"}}},"formula":"uv_dose_rate_j_m2_per_min = uv_index × 0.025 W/m² × 60 s × (1 − shade_factor_percent / 100) = uv_index × 1.5 × (1 − shade_factor_percent / 100); minutes_to_burn_unprotected = med_j_m2 / uv_dose_rate_j_m2_per_min; minutes_to_burn_with_spf = minutes_to_burn_unprotected × spf","method":"UV index 1 equals 25 mW/m² of CIE erythemally weighted irradiance (WHO), i.e. 1.5 J/m² per minute. The MED values 200, 250, 300, 450, 600 and 1000 J/m² for Fitzpatrick types I–VI are typical literature values; measured protection from sunscreen is usually a third to a half of the label SPF because people apply 0.5–1 mg/cm² instead of the 2 mg/cm² used in SPF testing. Informational only, not medical advice.","sources":[{"name":"WHO (2002) Global Solar UV Index: A Practical Guide","url":"https://www.who.int/publications/i/item/9241590076","type":"standard","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Ultraviolet index","url":"https://en.wikipedia.org/wiki/Ultraviolet_index","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Fitzpatrick scale","url":"https://en.wikipedia.org/wiki/Fitzpatrick_scale","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"UV index 8, skin type II, SPF 30","inputs":{"uv_index":8,"skin_type":"type_2","spf":30},"expected":{"minutes_to_burn_unprotected":20.8,"minutes_to_burn_with_spf":625,"hours_with_spf":10.42,"med_j_m2":250,"uv_dose_rate_j_m2_per_min":12,"uv_index_category":"Very high (8–10)"},"url":"https://tttkmbb.com/api/v1/calculate/uv-exposure-time?uv_index=8&skin_type=type_2&spf=30"},{"name":"UV index 5, skin type IV, 50 % shade, SPF 15","inputs":{"uv_index":5,"skin_type":"type_4","spf":15,"shade_factor_percent":50},"expected":{"minutes_to_burn_unprotected":120,"minutes_to_burn_with_spf":1800,"uv_dose_rate_j_m2_per_min":3.75,"uv_index_category":"Moderate (3–5)"},"url":"https://tttkmbb.com/api/v1/calculate/uv-exposure-time?uv_index=5&skin_type=type_4&spf=15&shade_factor_percent=50"}],"faq":[{"q":"Why is the SPF time unrealistic?","a":"SPF is measured with 2 mg/cm² of product; typical use is a quarter to half of that, and sweat, water and rubbing remove it. Reapply every 2 hours and treat the SPF time as an upper bound, not a plan."},{"q":"Is the UV index constant during the day?","a":"No. The forecast value is the daily maximum around solar noon; the dose rate is much lower in the morning and late afternoon, so the burn time computed from the peak index is conservative for those hours."},{"q":"What is a minimal erythema dose?","a":"The smallest UV dose that produces just-perceptible reddening 24 hours later. It rises from about 200 J/m² (type I) to 1000 J/m² (type VI) but varies about two-fold between people of the same type."}],"tags":["uv index","time to sunburn","skin type","spf","minimal erythema dose","sun exposure"],"related":[{"calculator_id":"heat-index","reason":"Apparent temperature for the same outdoor conditions."},{"calculator_id":"water-intake","reason":"Fluid needs on a hot day outdoors."}],"links":{"html":"https://tttkmbb.com/health/uv-exposure-time","markdown":"https://tttkmbb.com/health/uv-exposure-time.md","json":"https://tttkmbb.com/health/uv-exposure-time.json","api":"https://tttkmbb.com/api/v1/calculate/uv-exposure-time","schema":"https://tttkmbb.com/api/v1/calculators/uv-exposure-time","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:49:32Z","next_actions":[{"tool":"run_calculator","calculator_id":"uv-exposure-time","reason":"Run UV Exposure Time Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/health/uv-exposure-time.md"}}