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Heat Index Calculator

NOAA Rothfusz formula — calculate feels-like temperatures using humidity or dew point inputs, with OSHA safety guides.

Environmental Inputs

Air Temperature

Unit

Humidity Source

Relative Humidity (%)

Heat Index Reference Grid (°F)

Air Temp	40% RH	50% RH	60% RH	70% RH	80% RH	90% RH
80°F	81°	83°	85°	87°	90°	94°
85°F	86°	89°	92°	97°	103°	109°
90°F	92°	97°	103°	110°	119°	129°
95°F	100°	107°	116°	127°	140°	154°
100°F	111°	121°	133°	147°	164°	183°
105°F	123°	136°	152°	171°	192°	216°
110°F	137°	154°	174°	198°	225°	254°

Feels-Like Temperature

116.3°F

46.9°C

Calculated RH:60.0%

Risk Level:Danger

OSHA / NWS Protective Guide

Heat cramps or exhaustion likely; heat stroke possible. Reduce heavy physical activity, monitor workers, stay in air conditioning.

Dew Point Conversion: The calculator applies the Magnus-Tetens formula to determine relative humidity from dew point and air temperature variables.

NOAA Rothfusz Heat Index Methodology

The heat index is derived using a multi-parameter regression formula developed by the U.S. National Weather Service. It measures how the human body experiences temperature in high-humidity conditions, where sweat evaporation is slowed.

At temperatures below 80°F (27°C), a simplified linear index is applied. OSHA safety guidelines recommend scheduling hydrated breaks in shaded shelters when index limits trigger Caution thresholds.

Private & free — this tool runs entirely in your browser.