- Heat index
- 105.92 °F
How it works
Lower humidity can still feel hotter
A falling relative-humidity percentage does not by itself mean a lower heat index. Compare complete temperature-and-humidity pairs: hotter air can have a lower humidity percentage yet produce a higher apparent temperature under this model.
Understanding an apparent-temperature estimate
Heat index combines temperature with humidity under the selected reference method. The dew-point mode obtains humidity-related information from a different input pair, so check that the measurements describe the same conditions. The resulting index is not a complete measure of personal heat stress. Sun exposure, exertion, and individual circumstances are not all represented by the displayed number.
Heat index: formula and assumptions
Use the NWS simple estimate, then the Rothfusz regression and humidity adjustments when indicated.
Heat index assumes shade and light wind. Direct sun and other conditions can increase heat stress.
From temperature & dew point: formula and assumptions
Infer relative humidity with the Magnus model, then apply the NWS heat-index method.
Dew point cannot exceed air temperature. The heat index assumes shade and light wind.
Worked example
Using the Heat index example:
- Air temperature (°F)
- 90
- Relative humidity (%)
- 70
Use the NWS simple estimate, then the Rothfusz regression and humidity adjustments when indicated.
Example result
Heat index: 105.92 °F
These are illustrative inputs. Change the values to explore a different scenario.
Formula references
References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.
Common questions
Does the heat index include direct sunshine?
The model assumes shade and light wind. Direct sun and other conditions can increase heat stress beyond the displayed estimate.
Can the dew point be higher than the air temperature?
Not in this supported input model. A dew point above the air temperature is rejected rather than used as a valid humidity estimate.
Prepared by Finflo. See our methodology and editorial policy.