Dew Point Calculator
Calculate the dew point — the temperature at which air becomes saturated and dew forms — from air temperature and relative humidity using the Magnus formula. Results include °C and °F, the temperature-dew point spread, absolute humidity, and a comfort classification.
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Dew Point
13.2 °C
55.8 °F at 20 °C and 65% RH — Comfortable — pleasant for most people
Humidity analysis
- Air Temperature
- 20 °C (68 °F)
- Relative Humidity
- 65 %
- Dew Point
- 13.22 °C (55.79 °F)
- Spread (T − Td)
- 6.8 °C
- Saturation Pressure
- 23.33 hPa
- Vapor Pressure
- 15.16 hPa
- Absolute Humidity
- 11.21 g/m³
Dew point comfort scale (°C)
13.2°C
Comfortable
Magnus formula working
- 11. Compute αα = ln(RH/100) + 17.62·T/(243.12+T) = ln(0.65) + 17.62×20/263.12 = 0.9085
- 22. Solve for dew pointTd = 243.12·α/(17.62−α) = 243.12×0.9085/16.7115 = 13.22 °C
- 33. Interpret the spreadT − Td = 6.8 °C — air would need to cool 6.8 °C more for dew to form
The Magnus formula (a = 17.62, b = 243.12 °C) is accurate within ±0.35 °C from −45 to +60 °C. Dew point below ~55 °F (13 °C) feels comfortable; above 70 °F (21 °C) most people find it muggy.
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Formula
α = ln(RH/100) + 17.62·T/(243.12+T) → Td = 243.12·α/(17.62−α)
Pro tips
- • Small spread (T − Td < 3 °C) means fog, mist or heavy dew is likely.
- • For indoor comfort target 40–60% RH — about 10–16 °C dew point at 22 °C.
FAQ
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