UV Index Calculator for Burn Time & SPF
Estimate time to first visible redness by UV Index and Fitzpatrick skin type, compare SPF scenarios, and read a WHO-based UV Index chart.
Educational Use Only — Not Medical Advice
Results are estimates based on generalised models (WHO UV guidance, Fitzpatrick scale). They are not a guarantee of safe exposure. Actual skin response depends on cloud cover, altitude, reflective surfaces, medication, and individual variation. Consult a dermatologist for personal guidance. People with skin conditions, history of skin cancer, or photosensitivity should seek medical advice before sun exposure.
How to Use the UV Index Calculator
- Enter the current UV Index from your local weather forecast.
- Select the Fitzpatrick skin type that best matches how your skin usually reacts to sunlight.
- Add your planned time outdoors, sunscreen SPF, and the approximate area of exposed skin.
- Review the estimated unprotected time, UV risk level, sunscreen guidance, and vitamin D estimate.
Example: UV Index 7 with fair skin
Enter UV Index 7, choose your skin type, and set the planned exposure duration. The calculator compares the estimated UV dose with the skin type's erythema threshold and shows a personalized estimate. Treat the result as educational guidance—not a guarantee that sunburn will not occur.
UV Index Burn-Time Chart by Fitzpatrick Skin Type
This UV Index chart shows the calculator model's estimated minutes to a minimum erythemal dose—the threshold associated with first visible redness—on unprotected skin. It is an educational comparison, not a safe tanning or exposure schedule.
| UV Index | Risk | Type 1 | Type 2 | Type 3 | Type 4 | Type 5 | Type 6 |
|---|---|---|---|---|---|---|---|
| 2 | Low | ~67 min | ~83 min | ~117 min | ~150 min | ~200 min | ~333 min |
| 3 | Moderate | ~44 min | ~56 min | ~78 min | ~100 min | ~133 min | ~222 min |
| 5 | Moderate | ~27 min | ~33 min | ~47 min | ~60 min | ~80 min | ~133 min |
| 7 | High | ~19 min | ~24 min | ~33 min | ~43 min | ~57 min | ~95 min |
| 10 | Very High | ~13 min | ~17 min | ~23 min | ~30 min | ~40 min | ~67 min |
| 11 | Extreme | ~12 min | ~15 min | ~21 min | ~27 min | ~36 min | ~61 min |
Model: time = skin-type MED ÷ erythemally weighted dose rate; one UV Index unit equals 0.025 W/m². Protection is recommended when the UV Index reaches 3. Individual response may be faster because of photosensitising medicines, altitude, reflection, and other factors.
How Is the UV Index Calculated?
Weather services measure ultraviolet radiation across the wavelengths that affect skin, weight each wavelength by its erythemal effect, and combine the result into the UV Index. By definition, UV Index = 40 × erythemally weighted UV irradiance in W/m². This calculator reverses that relationship to estimate dose per minute, then compares the dose with a Fitzpatrick skin-type threshold.
WHO UV Index Scale
Frequently Asked Questions
How is the UV Index calculated?▼
How should I use the UV Index burn-time chart?▼
What is the UV Index and where can I find it?▼
What is the Fitzpatrick skin type scale?▼
What SPF sunscreen should I use for my skin type?▼
How does sun exposure produce vitamin D?▼
Can I get vitamin D through a window?▼
Does cloud cover reduce UV exposure?▼
Scientific References
- World Health Organization. Global Solar UV Index: A Practical Guide. WHO/SDE/OEH/02.2. Geneva: WHO; 2002.
- Holick MF. “Vitamin D deficiency.” New England Journal of Medicine 2007;357(3):266–281.
- Webb AR, Kline L, Holick MF. “Influence of season and latitude on the cutaneous synthesis of vitamin D₃.” J Clin Endocrinol Metab 1988;67(2):373–378.
- Schalka S, Steiner D, et al. “SPF: An important distinction between in vitro and in vivo.” Journal of Cosmetic Dermatology 2012;11(1):1–7.
- Fitzpatrick TB. “The validity and practicality of sun-reactive skin types I through VI.” Archives of Dermatology 1988;124(6):869–871.
- ICNIRP. “Guidelines on limits of exposure to ultraviolet radiation of wavelengths between 180 nm and 400 nm.” Health Physics 2004;87(2):171–186.