Heat Index Chart

How to Use a Heat Index Chart

Locate today’s predicted high temperature across the top column (Air Temp.). Down the left side (Relative Humidity), locate today’s predicted humidity. Follow across and down to find the “Apparent Temperature”. Keep in mind, this heat index chart was devised for shady, light wind conditions, so exposure to full sun can increase values by up to 15°F. Strong winds, particularly with hot, dry air can be extremely hazardous.

Air Temp.	70°F 21°C	75°F 24°C	80°F 26°C	85°F 29°C	90°F 32°C	95°F 35°C	100°F 38°C	105°F 41°C	110°F 43°C
Relative Humidity	Apparent Temperature (What it Feels Like) (Degrees Fahrenheit/Degrees Celsius)
0%	64°/18°	69°/21°	73°/23°	78°/25°	83°/28°	87°/30°	91°/33°	95°/35°	99°/37°
10%	65°/18°	70°/21°	75°/24°	80°/26°	85°/29°	90°/32°	95°/35°	100°/38°	105°/41°
20%	66°/18°	72°/22°	77°/25°	82°/27°	87°/30°	93°/34°	99°/37°	105°/41°	112°/44°
30%	67°/19°	73°/23°	78°/25°	84°/28°	90°/32°	96°/35°	104°/40°	113°/45°	123°/51°
40%	68°/20°	74°/23°	79°/26°	86°/29°	93°/34°	101°/38°	110°/43°	122°/50°	137°/58°
50%	69°/21°	75°/24°	81°/27°	88°/31°	96°/35°	107°/42°	120°/49°	135°/57°	150°/66°
60%	70°/21°	76°/24°	82°/27°	90°/32°	100°/38°	114°/45°	132°/56°	149°/65°
70%	70°/21°	77°/25°	85°/29°	93°/34°	106°/41°	124°/51°	144°/62°
80%	71°/22°	78°/25°	86°/29°	97°/36°	113°/45°	136°/58°	157°/69°
90%	71°/22°	79°/26°	88°/31°	102°/39°	122°/50°	150°/66°	170°/77°
100%	72°/22°	80°/26°	91°/33°	108°/42°	133°/56°	166°/74°

Likelihood of heat disorders with prolonged exposure or strenuous activity:

Heat Index	Risk Level	Protective Measures
Less than 91°F (32°C)	Lower (caution)	Basic heat safety and planning
91° to 103°F (32° to 39°C)	Moderate	Implement precautions and heighten awareness
103° to 115°F (39° to 46°C)	High	Additional precautions to protect workers
Greater than 115°F (46°C)	Very high to extreme	Triggers even more aggressive protective measures