Heat Index Calculator - calculatorsee.com


Heat Index Calculator

Calculate the summer Heat Index ("feels like" temperature) and heat illness danger level from air temperature and relative humidity.

Calculator Inputs

°F
Shade air temperature (>= 80°F).
%
Atmospheric relative humidity.

Calculated Results

Heat Index ("Feels Like")
95.0°F (35.0°C)
Danger Classification Extreme Caution
Apparent Increase +7.0°F above air temp
Heat Illness Risk Heat cramps and exhaustion possible with prolonged exposure
Values calculate live as you adjust inputs.

About Heat Index Calculator

Computes the apparent "feels like" temperature combining air temperature and relative humidity based on the NOAA / Rothfusz multiple regression equations.

What is Heat Index Calculator?

Computes the apparent "feels like" temperature combining air temperature and relative humidity based on the NOAA / Rothfusz multiple regression equations.

How to Use This Calculator

  1. Enter air temperature in °F (80°F or above).
  2. Select relative humidity.
  3. Read heat index and safety warning category.

The Mathematical Formula & Variables

Rothfusz 9-parameter polynomial regression equation

Step-by-Step Worked Example

Scenario: 88°F air temperature with 65% relative humidity.

  1. Calculated NOAA Heat Index = 95.0°F.
  2. Falls into the "Extreme Caution" category (90°F–103°F).

Result: Heat Index: 95.0°F (Extreme Caution)

Frequently Asked Questions

Why does high humidity make air feel hotter?

High humidity slows down the evaporation of sweat from human skin, impairing the body’s natural evaporative cooling mechanism.