Dew Point Calculator
°C
Unit
60%
Dew Point16.7°C / 62.0°F
Comfort LevelSlightly humid
The dew point is the temperature at which air becomes saturated and water vapor starts to condense, and it is a far better gauge of how muggy the air actually feels than relative humidity alone. This calculator takes the current air temperature and relative humidity and applies the Magnus approximation to return the dew point in both Celsius and Fahrenheit, along with a plain-language comfort rating from dry to very humid.
Formula
γ = (17.27·T)/(237.7 + T) + ln(RH/100); Td = (237.7·γ)/(17.27 − γ)
- T
- Air temperature in degrees Celsius
- RH
- Relative humidity as a percentage (0–100)
- γ
- Intermediate term combining temperature and humidity
- Td
- Dew point temperature in degrees Celsius
How it works
- Enter the air temperature and toggle whether it is in Celsius or Fahrenheit; Fahrenheit inputs are converted to Celsius internally before the calculation.
- Enter the relative humidity as a percentage between 0 and 100 (it must be greater than 0 for a valid result).
- The Magnus formula returns the dew point in Celsius, which is also converted to Fahrenheit, and a comfort band is assigned (Dry below 10°C, Comfortable up to 15°C, Slightly humid to 18°C, Humid to 21°C, and Very humid above that).
Worked example
Air at 25°C with 60% relative humidity — a warm summer afternoon.
- γ = (17.27 × 25)/(237.7 + 25) + ln(0.60) = 1.6443 + (−0.5108) = 1.1335.
- Td = (237.7 × 1.1335)/(17.27 − 1.1335) = 269.43 ÷ 16.137 ≈ 16.7°C.
- Convert: 16.7 × 9/5 + 32 ≈ 62.0°F.
Dew point ≈ 16.7°C (62.0°F), rated Slightly humid.
Frequently asked questions
- How is dew point different from relative humidity?
- Relative humidity is a percentage relative to how much moisture the air could hold at its current temperature, so it changes as temperature changes even with the same moisture. Dew point is an absolute temperature that reflects the actual amount of water vapor present, which is why it better predicts mugginess.
- What dew point feels comfortable?
- Dew points below about 10°C (50°F) feel dry, the low-to-mid teens Celsius feel comfortable, and once the dew point climbs past roughly 18–21°C (mid-60s to 70°F) most people start to feel sticky and oppressive.
- Why does condensation form at the dew point?
- When a surface or air parcel cools to the dew point, the air is fully saturated and can no longer hold all its vapor, so the excess condenses into liquid water — that is the dew on grass, fog, or the film on a cold drink.
- How accurate is the Magnus formula?
- The Magnus approximation used here (with constants a = 17.27 and b = 237.7) is accurate to within a few tenths of a degree for typical surface conditions from roughly 0 to 60°C, which is more than precise enough for weather and comfort estimates.