WEATHERGLASS
TEMPERATURE
FORMULAS
Temperature
Temperature is a measure of the amount of molecular motion in an object or
substance such as the air. As the sun pumps more energy into the air, molecular
motion increases.
This is indicated by a higher temperature. The four most common
temperature scales are:
- Fahrenheit (F)
- This is the temperature unit of the english measurement system Water freezes at 32
degrees and boils at 212 degrees.
- Celsius (C)
- This is the temperature unit of the metric measurement system. Water freezes at 0
degrees and boils at 100 degrees.
- Kelvin (K)
- This is the unit that is used to express absolute temperature in the metric system.
Zero Kelvin is the lowest possible temperature.
(Note: "Degree" is not used when expressing temperature in
the Kelvin system.)
- Rankine (R)
- This is the unit that is used to express absolute temperature in the english system.
Zero degrees Rankine is the lowest possible temperature.
The formulas for converting between any two temperatures are as follows:
| Units | Formula |
| Units | Formula |
| |
| F to C | C = (F - 32) / 1.8 | | C to
F | F = 1.8 * C + 32 |
| F to K | K = (F - 32) / 1.8 + 273.15 | | C
to K | K = C + 273.15 |
| F to R | R = F + 459.67 | | C
to R | R = 1.8 * C + 491.67 |
| |
| K to R | R = 1.8 * K | | R
to K | K = R / 1.8 |
| K to F | F = 1.8 * (K - 273.15) + 32 | | R
to F | F = R - 459.67 |
| K to C | C = K - 273.15 | | R
to C | C = (R - 491.67) / 1.8 |
| |
Wind Chill
Wind chill is an indication of the cooling effect of the wind. When the wind is calm, a thin layer of warm air exists
around the skin.
When the wind is blowing, the moving air carries this warm air away.
This causes the body to loose heat as if the temperature was cooler than it actually is.
The wind chill temperature is the temperature, with no wind, that would produce the same cooling as the actual temperature with the actual wind.
The formula for calculating wind chill is:
Twc = 35.74 + 0.6215 * T - 35.75 * W0.16
+ 0..4275 * T * W0.16
|
Twc |
is the wind chill temperature in degrees Fahrenheit |
|
T |
is the actual temperature in degrees Fahrenheit and must be less than 50 degrees |
|
W |
is the wind speed in miles per hour and must be greater than 3 mph |
Heat Index
The heat index is an indication of the effect of humidity on the apparent temperature. The body cools itself by
perspiration.
When the perspiration evaporates, it carries away heat, thus cooling the body. As the humidity increases,
perspiration evaporates
more slowly and the body heats up. The formula for calculating the heat
index is rather long. It is an approximation based on multiple regression
analysis and is accurate to ±1.3 ºF::
| THI = |
-42.379 + 2.04901523 * T + 10.1433127 * H - 0.22475541 * T * H - 6.83783 * 10-3 * T2 |
| | - 5.481717 * 10-2 * H2 + 1.22874 * 10-3 * T2 * H +
8.5282 * 10-4 * T * H2 - 1.99 * 10-6 * T2 * H2 |
|
THI | is the heat index |
| T | is the actual temperature in degrees Fahrenheit and must be at least 80
degrees |
| H |
is the relative humidity expressed as a per cent (50% would be 50, not 0.50) and must be at least 40% |