Dew Point vs Relative Humidity
Relative humidity changes with temperature — warm air can hold more water vapor than cool air. This means a 50% humidity reading at 80°F contains much more water than 50% at 60°F. Dew point is the temperature at which air would need to be cooled to reach 100% humidity. It is an absolute measure of moisture content. A dew point of 60°F feels the same regardless of whether the air temperature is 70°F or 95°F. This makes dew point a more consistent measure of mugginess.
Dew Point Comfort Scale
| Dew Point | Comfort Level | Heat Index Effect |
|---|---|---|
| Below 50°F | Very comfortable | Minimal effect on heat index |
| 50-55°F | Comfortable | Slight increase |
| 55-60°F | Slightly humid | Noticeable increase |
| 60-65°F | Humid | Heat index 5-10°F above air temp |
| 65-70°F | Very humid, uncomfortable | Heat index 10-15°F above |
| 70°F+ | Oppressive | Heat index 15-20°F+ above, dangerous |
Why This Matters for the Heat Index
The heat index rises sharply as dew point increases. A 90°F day with dew point 60°F (moderate humidity) gives a heat index of about 97°F. The same 90°F with dew point 75°F (extreme humidity, typical of tropical regions or after heavy rain) gives a heat index above 115°F. This is why the combination of high temperature and high dew point is uniquely dangerous.
Calculate Heat Index
Use our heat index and dew point calculators to understand current conditions.