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Science & Weather · Weather

Heat Index, Wind Chill & Dew Point Calculator — Feels-like Temperature

Find how hot or cold it really feels. Enter the air temperature with the relative humidity (or the dew point) and the wind speed to get the heat index with its risk level, the wind chill, the dew point and how muggy it feels — using the US National Weather Service formulas, in °C or °F.

Also listed inHealth & Fitness

Your inputs

Quick start — try a typical case

%
km/h

Used for wind chill (only when it's 10 °C / 50 °F or colder).

Your result Live

Feels Like (Heat Index)

45.1 °C

113.1 °F · Danger — heat cramps or exhaustion likely, heat stroke possible

Heat Index
45.1 °C — Danger — heat cramps or exhaustion likely, heat stroke possible
Wind Chill
Applies at 10 °C (50 °F) and below with wind over 5 km/h (3 mph)
Dew Point
26.1 °C — oppressive

Heat index assumes shade and a light wind; in direct sunshine it can feel up to about 8 °C (15 °F) hotter. Drink water and rest in the shade when the heat index is high.

How this is calculated

Heat index: NWS Rothfusz regression in T(°F) and RH · Wind chill = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275TV^0.16 · Dew point (Magnus): γ = ln(RH/100) + 17.625T/(243.04 + T), Td = 243.04γ/(17.625 − γ)

T, RH
Air temperature and relative humidity (%)
V
Wind speed in mph (wind chill)

Humid heat feels hotter because sweat evaporates more slowly; the heat index is the National Weather Service's estimate of that 'feels like' temperature. Wind carries heat away from skin, so cold air feels colder — the wind chill. The dew point is the temperature at which the air would be saturated; it's a better guide to mugginess than relative humidity, and above about 21 °C most people find it uncomfortable.

Assumptions & sources

  • Heat index is for shade and a light breeze; wind chill for an adult face at about 1.5 m above ground.
  • Formulas are empirical fits — accurate to about ±1 °F within their range.
  1. 1The heat index equation (Rothfusz regression and adjustments) — NOAA National Weather Service — Weather Prediction Center
  2. 2Wind chill temperature index (2001) — NOAA National Weather Service
  3. 3Improved Magnus form approximation of saturation vapor pressure (Alduchov & Eskridge, 1996) — Journal of Applied Meteorology

Calculator ID SCI-WEATHER-001 · version 1.0.0

Common questions

What does 35 °C at 60 % humidity feel like?

About 45 °C (113 °F) by the NWS heat index — in the 'danger' band.

What dew point is uncomfortable?

Above about 18 °C (65 °F) most people notice the humidity; above 21 °C (70 °F) it's oppressive for many.

When does wind chill apply?

Only when the air is 10 °C (50 °F) or colder and the wind is over about 5 km/h (3 mph).