Heat Index Calculator
Calculate the NWS heat-index model from air temperature and relative humidity, with its low/high humidity adjustments.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Convert Celsius to Fahrenheit for the published coefficient convention, select the stated branch and convert the resulting index back.
NWS preliminary apparent temperature followed, when applicable, by the Rothfusz T°F/RH regression and humidity adjustments
Worked example
32°C and 60% relative humidity give an NWS heat-index estimate of about 37.1°C; the model does not include direct sun or a particular person’s response.
Assumptions and input details
Scoped to air temperatures 80–122°F. NWS shaded/light-wind environmental index, distinct from wet-bulb globe temperature and personal risk assessment. No safe exposure time, work-rest schedule or medical interpretation is supplied.
References: NWS: heat-index calculation
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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