Heat Stress Calculator

Four published "feels-like" formulas in one panel: the NOAA heat index for hot humid days, the Environment Canada wind chill for cold windy days, the dew point as a humidity summary, and apparent temperature for a single year-round "feels-like" value. Type the conditions, every card recomputes live. Pure client-side, no upload.

Educational use only. The values are population-level formulas calibrated for outdoor shade conditions. They are not medical advice. For work or exercise in extreme conditions, follow your local heat-stress or cold-injury protocol.

Units
°C
%
km/h
Presets

Heat Index

NOAA Rothfusz (1979)
— °C

—

Wind Chill

Environment Canada (2001)
— °C

—

Dew Point

Magnus (Alduchov-Eskridge)
— °C

—

Apparent Temperature

Steadman (1984)
— °C

—

NOAA heat index bands

The National Weather Service uses these bands to issue heat advisories. The values are the heat-index temperature, not the air temperature.

Band Heat index Effect
Caution27–32 °CFatigue possible with prolonged exposure.
Extreme caution32–41 °CHeat stroke, heat cramps, or heat exhaustion possible.
Danger41–54 °CHeat stroke likely with continued exposure.
Extreme danger54 °C +Heat stroke imminent with any exposure.

Dew point comfort bands

Dew point (not relative humidity) is the most direct comfort indicator: higher dew point = muggier air.

Dew point Comfort
Below 10 °CDry and comfortable.
10–15 °CComfortable.
15–18 °CNoticeably humid.
18–21 °CUncomfortable; muggy.
21–24 °CVery humid; oppressive.
24 °C +Severely uncomfortable; dangerous for many.
How the four formulas differ, and when to trust which

Heat index is the US summer default: air temperature weighted by relative humidity. It only fires above 27 °C and (mostly) above 40 % humidity. Below those, NOAA itself says "use the air temperature".

Wind chill is the US/Canada winter default: how much faster exposed skin loses heat under wind. It only fires below 10 °C and above 5 km/h wind. Above 10 °C the formula produces nonsense.

Dew point is the temperature at which the air becomes saturated. It depends only on temperature and humidity (no wind) and is the cleanest "how muggy is it" indicator. Below 0 °C the air is usually described as "dry" regardless of the reading.

Apparent temperature (Steadman 1984) is the original Australian "feels-like" value and the predecessor of the Canadian Humidex. It works year-round (no T/RH thresholds) and folds wind in directly.

The four are not interchangeable. Heat index is the right answer for "should I cancel the outdoor run at 3 pm?". Wind chill is the right answer for "should I cover the dog's ears?". Apparent temperature is the right answer for "what should I wear?".