Wind chill calculator

What is wind chill?

How cold it feels on exposed skin when wind carries body heat away. At 0°F with a 15 mph wind, it feels like −19°F.

What is the wind chill formula?

The National Weather Service formula from 2001: 35.74 + 0.6215T − 35.75V^0.16 + 0.4275T × V^0.16, with T in °F and V the wind speed in mph.

When does wind chill apply?

Only at 50°F or colder with wind above 3 mph. Outside that range the formula is not defined, and the calculator says so.

Does wind chill cool objects below the air temperature?

No. Wind makes skin and objects lose heat faster, but they cannot get colder than the air itself.

How do I read the table?

It shows the wind chill at your temperature for winds from 5 to 60 mph, the same range as the NWS wind chill chart.

What does the formula assume?

The National Weather Service describes wind chill as how cold people and animals feel outside. The 2001 method calculates the wind speed at 5 feet, the typical height of an adult face, lowers the calm-wind threshold to 3 mph, and assumes no effect from the sun, as on a clear night. In the formula T is the air temperature in °F, V is the wind speed in mph and the result is in °F. The calculator’s metric option uses the equivalent form with °C and km/h, with the same limits: 10°C (50°F) and 4.8 km/h (3 mph).

Worked example: 0°F with a 15 mph wind

First raise the wind speed to the power 0.16: 15^0.16 = 1.542. Then 35.74 + 0.6215 × 0 − 35.75 × 1.542 + 0.4275 × 0 × 1.542 = -19°F. The National Weather Service gives the same figure for these conditions and adds that exposed skin can freeze in 30 minutes at this wind chill. A milder case, 20°F with a 10 mph wind, works out to 9°F: the air is 20°F, but it feels about 11 degrees colder.

Common mistakes with wind chill

Entering the wind in the wrong unit: the formula expects mph, and 30 km/h typed as 30 mph gives 1°F at 20°F air, while the correct 30 km/h (18.6 mph) gives 5°F. Expecting a number above 50°F or in a light breeze: wind chill is defined only for 50°F or colder and winds above 3 mph. Adjusting the wind yourself: the formula already allows for the 5-foot height of a face, so use the wind speed as reported in the forecast or by the station. Counting on sun to cancel it: the formula assumes no sun, so it cannot tell you how a sunny afternoon feels. And treating it as the air temperature: a thermometer in the wind still reads the air temperature, and wind chill describes only how fast skin loses heat.

Wind chill at a glance

Computed with the formula above, in °F, rounded to the nearest degree:

• Air at 30°F: 5 mph → 25°F, 15 mph → 19°F, 30 mph → 15°F, 60 mph → 10°F
• Air at 20°F: 5 mph → 13°F, 15 mph → 6°F, 30 mph → 1°F, 60 mph → -4°F
• Air at 10°F: 5 mph → 1°F, 15 mph → -7°F, 30 mph → -12°F, 60 mph → -19°F
• Air at 0°F: 5 mph → -11°F, 15 mph → -19°F, 30 mph → -26°F, 60 mph → -33°F
• Air at -10°F: 5 mph → -22°F, 15 mph → -32°F, 30 mph → -39°F, 60 mph → -48°F
• Air at -20°F: 5 mph → -34°F, 15 mph → -45°F, 30 mph → -53°F, 60 mph → -62°F

The effect of wind levels off. Going from a 5 mph breeze to 15 mph at 10°F lowers the wind chill from 1°F to -7°F, a drop of 8 degrees, but doubling again from 30 to 60 mph at the same air temperature takes off only 7 more. This is the V^0.16 term in the formula: a small exponent means each extra mile per hour matters less than the one before.

What wind chill does not tell you

It is a single number for a bare face in shade and cannot account for clothing, wet skin, or activity. Wet clothing loses heat much faster than dry, which is not in the formula. Because it assumes a clear night, a sunny day will feel warmer than the number says. The number is also about heat loss from skin, so it does not change what temperature a car, a pipe or a pet bowl reaches; those only cool toward the air temperature, not below it. Use the figure to judge exposure risk and what to wear, and follow the National Weather Service warning guidance for dangerous cold.

Sources and related calculators

Sources: National Weather Service, “Wind Chill Chart” safety page (definition, formula, assumptions, valid range, the 0°F and 15 mph example). Related: heat index calculator, dew point calculator and water intake calculator.