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What is an Easy Wind Chill Calculatioin

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A strong wind can greatly increase the rate of heat loss in cold weather. Wind chill attempts to put a number to this effect, based on the effect of wind on exposed human skin. All you need to calculate wind chill at home is a measurement of temperature and wind speed. Both are available from weather forecasts, and you can even measure wind speed at home with nothing more complicated than small paper cups and plastic straws.

  1. 1

    Measure the temperature T. Use a thermometer or look up your location's current outdoor temperature on a weather prediction website. You can measure this in degrees Fahrenheit or Celsius, but read the next step carefully so you know which unit to use for wind speed.

    • Wind chill is undefined for temperatures above 50ºF (10ºC). If the temperature is higher, wind doesn't have much effect on apparent temperature.

  2. 2

    Look up or measure wind speed, V. You can find wind speed estimates for your area on most weather prediction websites, or by searching for "wind speed + (the name of your town)" online. If you have an anemometer or make one using the instructions below, you can measure the wind speed yourself. If your temperature measurement used ºF, use the wind speed measurement in miles per hour (mph). If you used ºC, use kilometers per hour (km/h) instead.[1] If necessary, use this website to convert from knots to km/h.

    • If you're using an official wind speed measurement taken at 33 ft (10 m), multiply it by 0.75 to get a rough estimate of the wind speed at 5 ft (1.5 m), a typical height for a human face.[2]
    • Wind below 3 mph (4.8 km/h) does not have a significant wind chill effect.

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  3. 3

    Enter these values into the formula. There have been several wind chill formulas over the years and in different regions, but we'll use the one currently used by the UK, US, and Canada, created by an international team of researchers.[3] Plug in your numbers to the formula below, replacing T with the temperature and V with the wind speed:[4]

    • If using ºF and mph: Wind chill temperature = 35.74 + 0.6215T - 35.75V 0.16 + 0.4275TV 0.16
    • If using ºC and km/h: Wind chill temperature = 13.12 + 0.6215T - 11.37V 0.16 + 0.3965TV 0.16

  4. 4

    Adjust for sunshine. Bright sunshine can raise the apparent temperature by as much as +10 to +18ºF (+5.6 to +10ºC). There's no official formula to measure this effect, but be aware that sunlight will make the air seem warmer than the wind chill formula suggests.

  5. 5

    Understand wind chill. Wind chill is an invented concept that describes how wind increases heat loss on exposed skin. In extreme conditions, this can be a major factor in how soon frostbite sets in. At a wind chill temperature below –19ºF (-28ºC), frostbite will occur on exposed skin within 15 minutes or less. Below -58ºF (-50ºC), exposed skin can freeze within 30 seconds.[5]

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  1. 1

    Find an online wind chill calculator. Try the calculators at the US National Weather Service, freemathhelp.com, or onlineconversion.com.

    • All of these calculators use the new wind chill formula adopted by the US and other countries in 2001. If you use a different calculator, try to find one that uses this formula; the old formula can give misleading results.

  2. 2

    Look up the temperature and wind speed. Both of these pieces of information are typically available from weather forecasts on websites, television and radio stations, and newspapers.

  3. 3

    Multiply the wind speed by 0.75. Unless the forecast specifies wind speed at ground level, multiply the speed by 0.75 to get a more accurate estimate of the wind speed at the height of a human face.

    • This estimate is based on the standard wind speed measurement height of 33 ft (10 m), and typical atmospheric conditions.[6] Using a wind speed measured at a height of 5 ft (1.5 m) is more accurate, but not usually available without your own anemometer.

  4. 4

    Enter the measurements into the calculator. Make sure you select the units (such as mph or ºC) that the measurements are written in. Click "OK" or a similar button, and you should see the new apparent wind chill temperature.

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  1. 1

    Decide whether to make or buy an anemometer . An anemometer is a tool for measuring wind speed. You can buy one online, or make a simple one yourself in about 30 minutes using the steps below.[7] If you bought one, skip down to the step in which you count the rotations – or just read the wind speed directly, if yours has a digital display.

  2. 2

    Punch holes in small paper cups. Take four small paper cups, and punch a single hole in each one, about ½ inch (1.25 cm) below the rim. Take a fifth cup, and puncture four evenly spaced holes, about ¼ in. (6 mm) below the rim, then punch a fifth hole in the center of its base.

    • You can use a pencil to punch these holes, if you don't have anything sharper.

  3. 3

    Construct one half of the basic shape. Stick a plastic straw into a single-hole cup, about 1 inch (2.5 cm) into it. Push the other end of the straw through two holes of the five-hole cup. Stick the free end of the straw into another single-hole cup. Turn the two single-hole cups so they are pointing in opposite directions, along the same plane as the straw. Staple the straw to the cup.

  4. 4

    Finish the basic shape. Repeat with another straw, putting it through the remaining two holes of the central five-hole cup. Rotate these two new cups until each cup opening is nearer the base of the next one. In other words, the top cup points right, the right cup points down, the bottom cup points left, and the left cup points up. Staple the straws and cups together.

  5. 5

    Make a base for the anemometer. Slide the two straws until all four cups are the same distance from the center. Stick a small pin through the intersection of the two straws. Stick the eraser end of a pencil through the hole in the base of the central cup, and push it gently onto the pin. You can now hold the anemometer by the pencil tip, and use it to measure wind speeds.

  6. 6

    Count the number of rotations the anemometer makes. Hold the anemometer upright in a windy area. Watch a single cup (draw on it with a marker if it makes it easier to follow) and count the number of times it rotates. Use a stopwatch or a friend watching the second hand of a clock to time 15 seconds, and stop you when the time is up. Multiply your count by four to get the number of revolutions per minute (rpm).

    • For greater accuracy, count the number of rotations in 60 seconds (and don't multiply by anything).

  7. 7

    Calculate the circumference. Measure the distance from one edge of the anemometer to the other to find the diameter of the rotating circle, d. The circumference of the circle, is equal to πd. This is the distance traveled in one revolution.

    • If you don't have a calculator, you can use 3.14 as an estimate of π, or even just 3 for a rough estimate.

  8. 8

    Calculate wind speed. Convert the circumference you calculated into a more useful unit for measuring wind speed (miles or kilometers). Multiply the result by the rpm you calculated to get the total distance traveled in one minute. Multiply the result by 60 to get the distance traveled in one hour (mph or km/h). Here are the full formulas in imperial and metric units:

    • Imperial: (__circumference__ inches/revolution) * (1/12 ft/inches) * (1/5280 miles/ft) * (__rpm__ revolutions/minute) * (60 minutes/hour) = __wind speed__ in miles per hour.
    • Metric: (__circumference__ centimeters/revolution) * (1/100000 kilometers/centimeter) * (__rpm__ revolutions/minute) * (60 minutes/hour) = __wind speed__ in kilometers per hour.

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  • Wind cools people and objects more quickly than they would cool in calm air. It does not cause their internal temperature to drop below the actual surrounding air temperature. In practical terms, this makes wind chill useful when talking about people or animals, but not with inanimate objects that don't generate their own heat.

  • Apparent temperature (rate of heat loss) is also affected by humidity, air pressure, physical exertion, and natural differences between individuals. There is currently no commonly used formula for taking these into account.[8]

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