Tool

Wind Chill Calculator

—^°F

Air temperature

Unit

Wind speed

Wind unit

How do you calculate wind chill?

Wind chill uses the 2001 North American formula, which combines air temperature and wind speed into an equivalent still-air temperature for exposed skin. It is only defined at or below 50 °F (10 °C) with wind above about 3 mph — outside that range there is no meaningful wind chill to report.

The formula

With temperature in °F and wind speed in mph:

WC = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275T × V^0.16

The V^0.16 term is the interesting part. It rises steeply at low wind speeds and flattens out at high ones, which is why the first few miles per hour take off more than the last twenty. Going from calm to 10 mph costs you more than going from 30 mph to 40.

The formula assumes an adult face at walking pace, at night, out of direct sun. Bright sunshine offsets a real part of it, and a covered body is not losing heat at the rate the number describes.

Where it stops being valid

Two limits, and this calculator respects both rather than printing a number anyway:

At or below 50 °F (10 °C). Above that the equation was never fitted and returns meaningless values.
Above about 3 mph. Below that there is no wind chill; with still air the answer is the air temperature.

Most weather apps simply stop displaying wind chill outside those bounds, which occasionally reads as a missing feature. It is the correct behaviour.

Frostbite exposure times

The reason forecasters lead with wind chill rather than air temperature is that it maps onto how long uncovered skin lasts.

National Weather Service guidance for dry, uncovered adult skin. Wet skin fails faster.
Wind chill	Frostbite on exposed skin in
−18 °F (−28 °C)	About 30 minutes
−33 °F (−36 °C)	About 10 minutes
−48 °F (−44 °C)	About 5 minutes

Which points at the right response. A low wind chill is about the skin you have left uncovered — face, ears, hands — so covering those beats adding another layer over skin that is already covered.

What to use the air temperature for instead

Wind chill describes heat loss from a person and applies to nothing else. Wind can bring an object to the air temperature faster, but never below it.

So for pipes, plants, paint, concrete and car batteries, use the air temperature and the exposure time. A pipe in a 5 °F wind chill at 20 °F air temperature still cannot go below 20 °F — the reasoning is in what temperature pipes freeze at, and the full explanation of the number itself is in wind chill explained.

Common questions

Why does this show no wind chill above 50 °F?

Because the formula is not defined there. The 2001 equation was fitted to cold conditions, and applying it to mild weather produces numbers that look plausible and mean nothing. Wind still cools you above 50 °F — it just is not the thing this equation describes, and inventing a figure would be worse than declining to.

What wind speed should I enter?

The sustained wind speed rather than the gust, which is what forecasts and weather stations report by default. Using gust speeds gives a figure that is true for a few seconds at a time. If your app shows both, the sustained figure is the one the formula was built around.

Does wind chill apply below 3 mph?

No. With essentially no air movement there is no wind chill to calculate, and the formula returns values above the air temperature, which is nonsense. Below about 3 mph the air temperature is the answer.

Is the old wind chill formula different?

Very. The 1945 formula produced substantially colder figures and was replaced in 2001 after research using human volunteers rather than the earlier water-freezing experiments. If you remember wind chills that sounded more dramatic, you are remembering the old formula rather than colder winters.

Can I use this for my dog, or my pipes?

No. The formula is calibrated for bare adult human skin. Wind matters to a dog, but the number was not calculated for one. And wind cannot cool a pipe below the air temperature at all, so pipes, plants, paint and car batteries all take the air temperature instead.

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