How the Wind Chill Calculator Works
On a cold day, the wind makes you feel colder than the thermometer says. Your body warms a thin layer of air next to your skin. Wind blows that layer away, so you lose heat faster. Wind chill is a number that says how cold the air feels to bare skin because of the wind. The Wind Chill Calculator finds it from the air temperature and the wind speed.
What you enter
- Air temperature: the temperature that a thermometer shows, in degrees Fahrenheit or Celsius.
- Wind speed: in miles per hour or kilometers per hour.
The formula
The calculator uses the formula that was adopted in 2001 by the United States National Weather Service and Environment Canada. It is based on tests with people in a wind tunnel. With the temperature T in degrees Fahrenheit and the wind speed V in miles per hour:
wind chill = 35.74 + 0.6215 x T - 35.75 x V^0.16 + 0.4275 x T x V^0.16
In Celsius and kilometers per hour, the same formula reads:
wind chill = 13.12 + 0.6215 x T - 11.37 x V^0.16 + 0.3965 x T x V^0.16
The calculator changes your units, applies the formula, and changes the answer back into your unit, so both give the same result.
When the formula applies
The formula is only valid when the air is at 50 °F (10 °C) or colder, and the wind is above 3 mph (about 5 km/h). If it is warmer, or almost calm, there is no wind chill, and the calculator gives you the air temperature. Do not use the formula for a light breeze in a mild climate.
A worked example
The air temperature is 30 °F, and the wind is 15 mph.
| Step | Value |
|---|---|
| Wind speed to the power 0.16 (15^0.16) | 1.5423 |
| 35.74 + 0.6215 x 30 | 54.39 |
| - 35.75 x 1.5423 | -55.14 |
| + 0.4275 x 30 x 1.5423 | +19.78 |
| Wind chill | 19.0 °F |
It feels 11 degrees colder than the thermometer says. In Celsius, a temperature of -20 °C with a wind of 30 km/h feels like -32.5 °C.
Wind chill table
The wind chill in °F, for different temperatures and wind speeds:
| Air temperature | 5 mph | 10 mph | 15 mph | 20 mph | 30 mph | 40 mph |
|---|---|---|---|---|---|---|
| 40 °F | 36 | 34 | 32 | 30 | 28 | 27 |
| 30 °F | 25 | 21 | 19 | 17 | 15 | 13 |
| 20 °F | 13 | 9 | 6 | 4 | 1 | -1 |
| 10 °F | 1 | -4 | -7 | -9 | -12 | -15 |
| 0 °F | -11 | -16 | -19 | -22 | -26 | -29 |
| -10 °F | -22 | -28 | -32 | -35 | -39 | -43 |
| -20 °F | -34 | -41 | -45 | -48 | -53 | -57 |
Chart: how much colder the wind makes it
The air is at 0 °F. The bars show how many degrees colder it feels at each wind speed.
5 mph ███████████████ 10.5 degrees colder 10 mph ██████████████████████ 15.9 degrees colder 15 mph ███████████████████████████ 19.4 degrees colder 20 mph ███████████████████████████████ 22.0 degrees colder 30 mph ████████████████████████████████████ 25.9 degrees colder 40 mph ████████████████████████████████████████ 28.8 degrees colder
The first breeze matters most. Going from 0 to 10 mph takes off almost 16 degrees, and going from 30 to 40 mph takes off only 3 more. This is because of the small power of 0.16 in the formula.
Frostbite risk
Frostbite is damage to skin and the tissue below it, when it freezes. The colder the wind chill, the faster it can happen on bare skin. This is a guide, based on the National Weather Service wind chill chart:
| Wind chill | Frostbite on bare skin can start in about | What to do |
|---|---|---|
| 0 °F to 32 °F (-18 °C to 0 °C) | Not likely for most people | Wear a warm coat, a hat and gloves. |
| Below 0 °F (-18 °C) | More than 30 minutes | Dress in layers, and cover ears, hands and face. |
| -18 °F (-28 °C) and colder | 30 minutes | Cover all exposed skin. |
| -35 °F (-37 °C) and colder | 10 minutes | Limit your time outside. |
| -55 °F (-48 °C) and colder | 5 minutes or less | Stay inside if you can. |
- Wind chill: 0 °F to 32 °F (-18 °C to 0 °C)
Frostbite on bare skin can start in about: Not likely for most people
What to do: Wear a warm coat, a hat and gloves. - Wind chill: Below 0 °F (-18 °C)
Frostbite on bare skin can start in about: More than 30 minutes
What to do: Dress in layers, and cover ears, hands and face. - Wind chill: -18 °F (-28 °C) and colder
Frostbite on bare skin can start in about: 30 minutes
What to do: Cover all exposed skin. - Wind chill: -35 °F (-37 °C) and colder
Frostbite on bare skin can start in about: 10 minutes
What to do: Limit your time outside. - Wind chill: -55 °F (-48 °C) and colder
Frostbite on bare skin can start in about: 5 minutes or less
What to do: Stay inside if you can.
-18 °F and colder ██████████████████████████████ 30 minutes -35 °F and colder ██████████ 10 minutes -55 °F and colder █████ 5 minutes
These times are only a guide. Young children, older people, and people with poor circulation can get frostbite sooner. Wet skin or wet clothes make it worse.
What wind chill does and does not tell you
- It applies to people and animals, because they lose body heat. It does not make objects colder. A car, a pipe or a bucket of water will not fall below the air temperature because of wind, although the wind can make them cool down faster.
- It assumes you are walking in the shade at about 3 mph, with your face to the wind. Strong sunlight can make it feel 10 to 18 degrees warmer.
- Frostbite depends on the actual cold. If the wind chill is very low, cover your skin, whatever the reason.
Tips for cold weather
- Dress in layers, with a windproof outer layer. Wind takes heat through thin clothes.
- Cover your head, ears, hands, feet and face. These lose heat and freeze first.
- Keep dry. Wet clothing takes heat from your body much faster.
- Watch for the signs of frostbite: skin that is numb, pale, waxy or hard. Get warm and get medical help.
- Watch the wind forecast, not only the temperature, before a long walk, ski or work outdoors.
What this calculator does not include
- Humidity, sunshine, and the clothes you wear.
- Air temperatures above 50 °F, and winds of 3 mph or less. There is no wind chill in these cases.
- The heat index, which describes hot weather.
This tool gives an estimate for general information only. It is not medical advice. In dangerous cold, follow the warnings of your local weather service.