Uv Index Calculator
Estimate UV radiation level and safe sun exposure time based on skin type and conditions. Enter values for instant results with step-by-step formulas.
Formula
UV Index = 12 x cos(zenith)^1.4 x altitude_factor x cloud_factor
The UV index is estimated from the solar zenith angle (based on latitude and month), adjusted for altitude (+7% per 1000m) and cloud cover (up to -75% reduction). Burn time is calculated from skin type sensitivity divided by UV index, then multiplied by SPF if sunscreen is applied.
Worked Examples
Example 1: Summer Beach Day at Mid-Latitude
Problem: Estimate the UV index at latitude 35N in July at sea level with clear skies. A person with Type II skin plans to be outdoors without sunscreen.
Solution: Solar declination in July: ~+20.6 degrees\nSolar zenith angle: |35 - 20.6| = 14.4 degrees\nBase UV = 12 x cos(14.4)^1.4 = 12 x 0.968^1.4 = 11.5\nNo altitude adjustment (sea level)\nNo cloud adjustment (clear skies)\nEstimated UV Index: 11.5 (Extreme)\nType II burn time: 100/11.5 = ~9 minutes unprotected
Result: UV Index: 11.5 (Extreme) | Unprotected burn time: ~9 minutes for Type II skin
Example 2: Mountain Hiking with Sunscreen
Problem: Estimate UV at latitude 40N in June at 2,500m elevation with 30% cloud cover. Hiker has Type III skin and applies SPF 30.
Solution: Solar declination in June: ~+23.1 degrees\nSolar zenith: |40 - 23.1| = 16.9 degrees\nBase UV = 12 x cos(16.9)^1.4 = 11.1\nAltitude factor: 1 + (2.5 x 0.07) = 1.175 -> UV = 13.0\nCloud reduction: 1 - (0.30 x 0.75) = 0.775 -> UV = 10.1\nType III burn time: 200/10.1 = ~20 minutes without sunscreen\nWith SPF 30: 20 x 30 = 600 minutes (~10 hours theoretical max)
Result: UV Index: 10.1 (Very High) | With SPF 30: ~10 hours protected (reapply every 2 hours)
Frequently Asked Questions
What is the UV Index and what does it measure?
The UV Index is an international standard measurement of the strength of ultraviolet radiation from the sun at a particular place and time. It was developed by the World Health Organization in collaboration with several international agencies to provide a simple number that indicates the potential for skin damage from sun exposure. The index ranges from 0 to 11 and above, with higher values representing greater risk of overexposure. Values of 1-2 are considered low, 3-5 moderate, 6-7 high, 8-10 very high, and 11 or above extreme. The UV Index specifically measures the erythemally weighted UV radiation, which accounts for the different biological effects of UVA and UVB wavelengths on human skin.
How accurate are the results from Uv Index Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.
Is Uv Index Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.
Can I use Uv Index Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
What formula does Uv Index Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.