Heat Index Chart - Apparent Temperature vs. Temperature & Relative Humidity

Oct 12, 2026

Heat Index Chart explains how “heat index” represents the apparent temperature the body experiences, derived from relative humidity and air temperature. Values apply to shaded locations, while full sunshine can raise heat index by up to 15°F. It also notes that strong winds with very hot, dry air can be extremely hazardous because wind adds heat. The chart categorizes risk levels from extremely hot to very warm, describing likely heat impacts for high-risk groups and exposure duration.

LanguageEnglish

CategoryGeneral

FormatPDF

Pages2

Reading Time1 min

AccessFree to download

Heat Index definition

Heat index vs. humidity and air temperature

Risk categories and general effects

Extremely hot

Very hot

Hot

Very warm

Additional hazard notes

Heat Index Chart The ‘Heat Index’ is a measure of how hot weather "feels" to the body. This table uses relative humidity and air temperature to produce the"apparent temperature" or the temperature the body "feels". These values are for shady locations only. Exposure to full sunshine can increase heat index values by up to 15°F. Also, strong winds, particularly with very hot, dry air, can be extremely hazardous as the wind adds heat to the body. Temperature & Relative Humidity | Classification | Heat Index/Apparent
Temperature | General Affect on People in High Risk Groups | | --- | --- | --- | | Extremely Hot | ≥130°F | Heat/Sunstroke HIGHLY LIKELY with continued exposure | | Very Hot | 105°F-129°F | Sunstroke, heat cramps, or heat exhaustion LIKELY, and heatstroke POSSIBLE with prolonged exposure and/or physical activity | | Hot | 90°F-104°F | Sunstroke, heat cramps, or heat exhaustion POSSIBLE with prolonged exposure and/or physical activity | | Very Warm | 80°F-89°F | Fatigue POSSIBLE with prolonged exposure and/or physical activity | Relative Humidity (%) [www.weather.gov/jetstream/hi](www.weather.gov/jetstream/hi) % 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100 % Temperature ( F) 126 124 122 120 118 116 114 112 110 108 106 104 102 100 98 96 94 92 90 88 86 84 82 80 78 76 | 113 | 116 | 119 | 123 | 126 | 130 | 134 | 138 | 142 | 147 | 151 | 156 | 161 | 166 | 171 | 177 | 182 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | 112 | 114 | 117 | 120 | 123 | 127 | 130 | 134 | 138 | 142 | 146 | 151 | 155 | 160 | 165 | 170 | 175 | 180 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 110 | 113 | 115 | 118 | 121 | 124 | 127 | 130 | 134 | 138 | 141 | 145 | 150 | 154 | 158 | 163 | 168 | 173 | 178 | 183 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 109 | 111 | 113 | 116 | 118 | 121 | 124 | 127 | 130 | 133 | 137 | 140 | 144 | 148 | 152 | 156 | 161 | 165 | 170 | 175 | 180 | | | | | | | | | | | | | | | | | | | | | | | | | | | WEAT | HER-R | EADY | NATION | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 107 | 109 | 111 | 113 | 116 | 118 | 121 | 123 | 126 | 129 | 132 | 135 | 139 | 142 | 146 | 150 | 154 | 158 | 162 | 167 | 171 | 176 | 181 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 106 | 108 | 109 | 111 | 113 | 115 | 117 | 120 | 122 | 125 | 128 | 131 | 134 | 137 | 140 | 144 | 148 | 151 | 155 | 159 | 164 | 168 | 172 | 177 | 182 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 105 | 106 | 107 | 109 | 111 | 112 | 114 | 117 | 119 | 121 | 124 | 126 | 129 | 132 | 135 | 138 | 141 | 145 | 148 | 152 | 156 | 160 | 164 | 168 | 173 | 177 | 182 | | | | | | | | | | | | | | | | | | | | | | | | | | | | 103 | 104 | 105 | 107 | 108 | 110 | 112 | 113 | 115 | 117 | 120 | 122 | 124 | 127 | 130 | 133 | 136 | 139 | 142 | 145 | 149 | 152 | 156 | 160 | 164 | 168 | 172 | 177 | 181 | | | | | | | | | | | | | | | | | | | | | | | | | | 101 | 102 | 103 | 104 | 106 | 107 | 109 | 110 | 112 | 114 | 116 | 118 | 120 | 122 | 125 | 127 | 130 | 133 | 136 | 139 | 142 | 145 | 149 | 152 | 156 | 159 | 163 | 167 | 171 | 175 | 180 | | | | | | | | | | | |

FAQs

What does the heat index measure?

Heat index measures how hot weather “feels” to the body as apparent temperature calculated from relative humidity and air temperature.

Do the chart values apply in direct sunlight?

No. The values are for shady locations only, and exposure to full sunshine can increase heat index values by up to 15°F.

How are high-risk heat impacts grouped in the chart?

The chart classifies heat levels (extremely hot, very hot, hot, very warm) and indicates whether sunstroke, heat cramps, or heat exhaustion are highly likely or possible, based on continued exposure and/or physical activity.

Oct 12, 2026

Uploaded by LangkahRina