The sunburn risk calculator estimates how long you can safely spend in the sun before burning, based on your UV index, skin type, and sunscreen SPF. Results are approximations — reapply sunscreen every 2 hours regardless of calculated time.
Calculate Your Burn Time
Check your local weather app or UV forecast
How to Use the Sunburn Risk Calculator
This sunburn risk calculator uses your UV index, skin type, and SPF to estimate how long you can safely be in direct sunlight without significant burn risk.
Step 1: Find the UV Index
Check your local weather app, weather.gov, or a UV index forecast service. The UV index is highest between 10am and 4pm, especially in summer months. On overcast days, UV can still be 50-80% of clear-sky levels — clouds block visible light more than UV.
Step 2: Apply Sunscreen Correctly
For full SPF protection, apply 2mg per cm² of skin — about 1 oz (one shot glass) for a full body application. Most people apply far less. Applying half the recommended amount reduces effective SPF significantly (SPF 30 at half dose performs more like SPF 5-10).
Practical Sun Safety
Reapply sunscreen every 2 hours — UV degrades the active ingredients. Seek shade during peak hours (10am–4pm). Wear UPF-rated clothing, wide-brim hats, and UV-blocking sunglasses. Water, snow, and sand reflect UV and can increase exposure intensity beyond the UV index level.
FAQ
Is this sunburn calculator free?
Yes, completely free with no signup required.
How is burn time calculated?
The base burn time depends on skin type and UV index: Type I skin burns in about 67/UV-index minutes without protection. SPF multiplies this time — SPF 30 theoretically extends it 30x. In practice, SPF effectiveness is reduced by sweating, swimming, and incomplete application, so actual protection is typically 2-4 hours maximum.
What is the UV Index?
The UV Index (UVI) measures ultraviolet radiation intensity from 0 (no UV) to 11+ (extreme). Values above 3 warrant sunscreen; above 6 require it. Peak UVI occurs at solar noon (12pm-2pm) and is highest in summer, at altitude, near the equator, and on snow or water that reflects UV.
Does sunscreen block all UV rays?
No. SPF ratings apply to UVB rays (which cause sunburn). A broad-spectrum sunscreen also filters UVA rays (which cause aging and skin cancer) but SPF numbers don't quantify UVA protection. Reapply every 2 hours and after swimming or sweating — sunscreen breaks down with UV exposure.
What SPF should I use?
Dermatologists recommend SPF 30+ for most daily use (blocks about 97% of UVB). SPF 50 blocks about 98% and is recommended for outdoor activities, high UV index days, or fair skin. SPF above 50 provides minimal additional benefit. No sunscreen is truly waterproof — reapply after 40-80 minutes of water activity.