Heat Wave Risk Calculator

Estimate heat health risk during hot weather — especially for vulnerable groups in the UK.

Maximum daytime temperature (°C)

Minimum overnight temperature (°C)

Humidity (%)

Vulnerable group?

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Fill in the details to get your result.

How This Works

Heat risk is determined by three factors: (1) daytime peak temperature — above 30°C increases risk significantly, (2) overnight minimum — warm nights (18°C+) prevent the body from recovering, compounding heat stress over multiple days, (3) humidity — high humidity prevents sweat evaporation, the body's primary cooling mechanism. Risk is amplified substantially for the elderly, young children, and those with cardiovascular or respiratory conditions.

Heat exhaustion: heavy sweating, pale clammy skin, weakness, dizziness, nausea, headache, muscle cramps. Treatment: move to cool place, drink water, cool with damp cloth, loosen clothing. Usually resolves in 30 minutes. Heat stroke (medical emergency): body temperature above 40°C, hot dry skin (sweating may stop), confusion, slurred speech, loss of consciousness. Call 999 immediately. Cool the person by any means available while waiting for ambulance.