Worked example: Heat Index Calculator
90°F and 70% humidity. This fixed reference example shows one complete scenario; the interactive results above use your current inputs.
View the example inputs
- Temperature unit
- Fahrenheit
- Air temperature
- 90 °F
- Relative humidity
- 70 %
| Calculated quantity | Example result |
|---|---|
| Heat index | 41.1 °C |
| Heat index | 105.9 °F |
Understanding a weather index and its valid range
An index describes a particular model
Air temperature, humidity and wind can combine into different reference measures. Wind chill, heat index and dew point do not represent the same physical question. A formula valid for cold, windy conditions should not be extended to warm air, and a shaded heat estimate does not describe every exposure.
Check temperature units, wind units and humidity percentages before interpreting a result. Values at a model boundary can require a different equation or a rejection message rather than a simple continuation of the curve.
Interpret the conditions alongside the number
Direct sun, clothing, exertion, indoor conditions and individual physiology can change actual comfort and risk. A calculated weather index is not an individual exposure limit. A room-cooling chart is likewise a sizing estimate under stated building assumptions.
The linked source and formula identify the reference method. Use current local observations or an entered scenario as inputs; the calculator does not supply a live forecast.
Formula and calculation method
Uses the preliminary Steadman approximation and the Rothfusz regression when the preliminary average is at least 80°F, with NWS humidity corrections.
Assumes shade and light wind. Direct sun and individual health conditions can substantially change heat risk; this is not a work/rest or medical clearance tool.
Reference Sources
Frequently asked questions
How does this calculator work?
Uses the preliminary Steadman approximation and the Rothfusz regression when the preliminary average is at least 80°F, with NWS humidity corrections.
What assumptions should I check?
Assumes shade and light wind. Direct sun and individual health conditions can substantially change heat risk; this is not a work/rest or medical clearance tool.
Can I save or print this calculation?
Use Copy link with inputs to reproduce the scenario, Download results for a text record, or Print. Where a schedule is shown, its CSV download includes every row.
What happens when I change measurement units?
The linked unit selector converts the existing measurement so it represents the same physical quantity. Entering a different number after switching units changes the underlying input. The result’s own units are shown beside its value.