Everyday / Browser calculator

Heat Index Calculator

Heat Index Calculator works from the inputs you provide and returns regression heat index (°c), regression heat index (°f). Use the calculation panel to explore a scenario, then check the formula and limitations before applying the result.

Your inputs

Minimum: 26.6667 · Maximum: 60
Minimum: 0 · Maximum: 100

Your results

Enter your values and calculate to see the result.

Formula and calculation method

Rothfusz regression uses temperature T in °F and humidity R: HI = −42.379 + 2.04901523T + 10.14333127R − .22475541TR − .00683783T² − .05481717R² + .00122874T²R + .00085282TR² − .00000199T²R², with low/high humidity adjustments.

Hot-weather estimate for shade and light wind. Direct sun, exertion and individual health alter risk. Not a safety clearance.

How to use heat index calculator

  1. Set Temperature (°C). The example below uses 32.
  2. Set Relative humidity (%). The example below uses 70.
  3. Select Calculate to update the result. Reset restores the illustrated inputs. Copy, print or download your own result if you need a record.

Worked example

Example inputs
Temperature (°C)
32
Relative humidity (%)
70
Regression heat index (°C)
40.40927368
Regression heat index (°F)
104.73669262

Factors affecting your result

Hot-weather estimate for shade and light wind. Direct sun, exertion and individual health alter risk. Not a safety clearance.

Changing temperature (°c) changes the scenario being evaluated. Adjust one input at a time when comparing results, keep a copy of the assumptions, and compare values using the same unit and period. A precise arithmetic result does not make an uncertain assumption precise.

Frequently asked questions

How does the heat index calculator work?

Rothfusz regression uses temperature T in °F and humidity R: HI = −42.379 + 2.04901523T + 10.14333127R − .22475541TR − .00683783T² − .05481717R² + .00122874T²R + .00085282TR² − .00000199T²R², with low/high humidity adjustments.

What inputs does Heat Index Calculator need?

Enter temperature (°c), relative humidity (%). Read the unit labels; percentages are entered as ordinary percentages, not decimal fractions.

How should I interpret the heat index calculator result?

Hot-weather estimate for shade and light wind. Direct sun, exertion and individual health alter risk. Not a safety clearance.

Are my heat index calculator inputs uploaded?

No. The calculation runs in this browser. Favorites, recent tool names, theme and formatting preferences may be saved locally, but calculation inputs are not sent to a calculation server or stored by this website. Shared links do not include entered values.

Method reference

Maintained by Calculators.buzz Editorial Team. Implementation date: . No professional credentials or clinical review are claimed. Read our methodology policy.