Dew Point Calculator
Calculate the dew point temperature from air temperature and relative humidity.
Understand comfort levels and condensation risk.
The dew point is the temperature at which air becomes saturated with water vapor — causing moisture to condense out as dew, fog, or frost. It is a more reliable indicator of human discomfort than relative humidity alone.
Magnus formula approximation: Dew Point (°C) = (243.04 × [ln(RH/100) + (17.625 × T)/(243.04 + T)]) ÷ (17.625 − [ln(RH/100) + (17.625 × T)/(243.04 + T)])
Where:
- T = air temperature in °C
- RH = relative humidity in percent
- ln = natural logarithm
Simplified approximation (accurate within 1°C for RH > 50%): Dew Point ≈ T − ((100 − RH) / 5)
Worked example: Temperature: 28°C | Relative Humidity: 75% Dew Point ≈ 28 − ((100 − 75) / 5) = 28 − 5 = 23°C
Human comfort scale by dew point:
| Dew Point | Comfort Level |
|---|---|
| Below 10°C (50°F) | Very comfortable, dry |
| 10–16°C (50–61°F) | Comfortable |
| 16–18°C (61–65°F) | Slightly humid |
| 18–21°C (65–70°F) | Noticeably humid, some discomfort |
| 21–24°C (70–75°F) | Oppressive, heavy |
| Above 24°C (75°F) | Extremely oppressive, dangerous |
Dew point vs. relative humidity: RH of 80% on a cold 5°C day feels dry and crisp. RH of 60% on a hot 35°C day feels muggy and uncomfortable. Dew point above 21°C (70°F) is uncomfortable regardless of temperature — which is why meteorologists prefer it as a humidity metric.