What UV index is dangerous?

UV 1-2: Low risk. UV 3-5: Moderate (sunscreen recommended). UV 6-7: High (protection essential). UV 8-10: Very high (avoid midday sun). UV 11+: Extreme (avoid outdoor exposure). In the UK, summer UV typically reaches 6-8 on clear days, and up to 9-10 during heatwaves.

Does altitude affect UV exposure?

Yes, significantly. UV increases by approximately 10% for every 1,000m of altitude gain. At 3,000m (e.g. many Alpine peaks), UV is 30% stronger than at sea level. Snow reflection can double UV exposure. Mountain hikers burn much faster than lowland walkers.

How often should I reapply sunscreen?

Reapply every 2 hours as a maximum, or more frequently if sweating heavily, swimming, or towelling off. Apply generously — most people use only 25-50% of the recommended amount. For a full body application, use approximately 35ml (a shot glass full).

What SPF should I use for hiking?

SPF 30 blocks 97% of UVB rays and is sufficient for most UK conditions. SPF 50 blocks 98% and is recommended for high altitude, snow, or fair skin. Above SPF 50, the additional protection is minimal. More important than high SPF is thorough and frequent application.

CampCalcs

UV Exposure Calculator

Estimate safe sun exposure time based on UV index, skin type and altitude.

UV Index

Check Met Office forecast

Skin TypeEnter the skin type

Altitude

Enter the altitude

Sunscreen SPF

Enter the sunscreen spf

How We Calculate This

Burn Time Calculation

Burn time = Base time for skin type / UV index / Altitude factor

Altitude factor = 1 + (Altitude in m / 1000) x 0.10

SPF Protection

Protected time = Burn time x SPF value

Reapply at 70% of protection time, or every 2 hours maximum.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.