Heat index chart
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Heat index
— °FAdd your readings for an estimate.
No location lookup or live weather.
Not medical advice. No result is a safety clearance. Follow official local and workplace guidance.
Read the band, not just the number
No band until a supported calculation is made.
- Caution
80–<90°F - Extreme caution
90–<103°F - Danger
103–<125°F - Extreme danger
125°F+
Ordered position, patterns and a “Current band” label identify the result. Below these bands is not safe.
Your calculation record
Not medical advice.
Calculated reference matrix
Rows: air temperature in your chosen unit. Columns: relative humidity (%). Select a cell for a single answer above. Scroll horizontally inside the table on narrow screens, or use the row-by-row text alternative below. A dash means the combination is outside this site's supported output range.
No cell selected.
Row-by-row text alternative (no horizontal scrolling)
Not medical advice. Estimates only; follow official local and workplace guidance.
Not medical advice
A heat-index chart combines air temperature and relative humidity. Read across from the temperature and down from the humidity to find their combined apparent temperature.
This is a small reference table for comparison, not a complete forecast or a chart of safe exposure times. For a value between its rows and columns, enter the actual readings in the heat-index calculator.
A quick reference in Fahrenheit
Each interior value is a calculated heat index in °F, rounded to the nearest whole degree using the NWS method. The row labels are air temperatures, not heat-index values.
| Air temperature | 40% RH | 60% RH | 70% RH |
|---|---|---|---|
| 80°F | 80 | 82 | 83 |
| 85°F | 84 | 89 | 93 |
| 90°F | 91 | 100 | 106 |
| 95°F | 99 | 113 | 123 |
Humidity has a larger effect as the air gets hotter. A five-degree change in air temperature does not imply a five-degree change in heat index.
Why another chart might look slightly different
Printed charts usually round values and show a limited range of inputs. A calculator can retain decimal values, apply humidity adjustments and use the NWS simple-method branch when conditions do not call for the hot-weather regression.
The official NWS equation is the method behind this table. The main calculator explains the risk bands. Do not extrapolate the rows to extreme conditions; the Rothfusz regression is not validated for every imaginable temperature and humidity combination.
Shade is part of the meaning
These values describe shade and light wind. Direct sunshine, exertion, protective clothing and radiant heat are not extra columns hidden in the table. Their absence limits what the chart can tell you.
For workplace activity, use an assessment that reflects the actual site. OSHA's guidance explains why heat index can underestimate occupational heat stress. If someone develops symptoms, respond to the person rather than waiting for the table to reach a particular color.
Method and transparency
Last updated: 6 November 2026. Not medical advice.