# Heat Index (HI) Calculator

Heat Index (HI) Calculator

°F

%

Heat Index (HI) Calculator Results
Fahrenheit (°F)Celsius (°C)Kelvin (K)
Heat Index (HI):---
Heat Index Chart (Apparent Temperature)
Temperature (°F)Relative Humidity (%)
404550556065707580859095100
110136143152161171182194206219233247262278
108130137144153162172182193205218231245260
106124130137145153162172182193204216229243
104119124131137145153161171181191202214226
102114119124130137144152160169179189199210
100109114118124129136143150158167176185195
98105109113117123128134141148156164172181
96101104108112116121126132138145152160168
9497100102106110114119124129135141148155
92949699101105108112116121126131137143
9091939597100103106109113117122127132
88888991939598100103106110113117121
868587888991939597100102105108112
848384858688899092949698100103
8281828384848586888990919395
8080808181828283848485868687
 Classification: Very Warm Hot Very Hot Extremely Hot

Heat Index (HI) Calculator will help you calculate the heat index (HI) based on air temperature (T) and relative humidity (RH).

## How to use the Heat Index (HI) Calculator

1. Select the “Temperature Units” from drop-down list;

2. Enter the “Air Temperature”;

3. Enter the “Relative Humidity”;

4. Click on the “Calculate” button to get the results.

## Heat Index (HI) Calculator

HI (Heat Index, °F) = C1 + C2 T + C3 RH + C4 T RH + C5 T2 + C6 RH2 + C7 T2 RH + C8 T RH2 + C9 T2 RH2 + CF

HI means the heat index (°F);

T means the air temperature in Fahrenheit (°F);

RH means the relative humidity (%);

CF means the correction factor;

C1 = -42.379;

C2 = 2.04901523;

C3 = 10.14333127;

C4 = -0.22475541;

C5 = -6.83783 × 10 -3;

C6 = -5.481717 × 10 -2;

C7 = 1.22874 × 10 -3;

C8 = 8.5282 × 10 -4;

C9 = -1.99 × 10 -6.

If 80°F ≤ T ≤ 112°F, RH ≤ 13%; CF (Correction Factor) = – ([13 – RH] / 4) × ([17 – |T – 95|] / 17)0.5

If 80°F ≤ T ≤ 87°F, RH > 85%; CF (Correction Factor) = 0.02 × (RH – 85) × (87 – T)