How to Compute the Heat Index

By determining the heat index, you know not only how hot it is outside but also how hot it feels. There is some information that you need to complete the formula, and the accuracy of the heat index that you compute will largely depend on your mathematical ability.

Instructions

Difficulty: Moderate

Things You’ll Need:

• Thermometer
• Calculator

1. Use a thermometer to determine the temperature outside. Depending on the formula that you choose, you may need to use different types of temperature degrees such as Kelvin, Fahrenheit and Celsius. For the purposes of this formula, you need to know the temperature in Celsius.
2. Determine the relative humidity outside. Consult a newspaper or weather website, or you can calculate your own relative humidity by using a formula to help you. The formula can be fairly complicated if you aren't very familiar with higher-level mathematics. If you find that the formula is intimidating, then you can get this information from another source.
3. Use the following formula: HI = T + (5/9)(e – 10). Note that HI is heat index, T is the temperature and e is the vapour pressure.
4. Calculate e, which is the vapour pressure with the following equation: e = ((6.112 X 10)(7.5T)/(237.7 + T))(R/100). Note that R is the relative humidity. As with the formula to determine the relative humidity, you might want to consult another source if you find that this formula is intimidating to you.
5. Input the numbers for T, the temperature and e, the vapour pressure.
6. Do the calculations and determine the heat index outside. You can also consult online calculators that will help you.

Tips & Warnings

• Scientific calculators can help you compute complicated formulas.
• Be sure that all of the variables are correct. If one is wrong, your end result will also be wrong.