Sustainability checks

Heat Index Calculator

Calculate the apparent 'feels like' temperature considering both heat and humidity. Use this Environment and sustainability tool to enter your numbers, review the result, and understand the key assumptions before making the next decision.

What you get
A focused calculator, clear explanation, common questions, and useful next tools.
Quick intro
Calculator
Result
Explanation
Common questions
Related tools

Calculator tool

How this calculator works
The result depends on the numbers you enter and the assumptions shown below.

The heat index (Rothfusz equation) applies when T ≥ 80°F and RH ≥ 40%. High humidity prevents sweat evaporation, trapping body heat. Heat index above 103°F is dangerous.

Review the inputs carefully and treat the output as an estimate. For decisions involving money, taxes, health, law, or security, compare the result with trusted professional guidance when needed.

Frequently asked questions

When is heat index dangerous?

Above 91°F: caution; above 103°F: danger; above 125°F: extreme danger. Prolonged exposure can cause heat cramps, exhaustion, and heat stroke.