Dew Point Calculator
Calculate dew point from air temperature and relative humidity using the Magnus formula. Get absolute humidity, comfort assessment, and HVAC condensation risk.
°F
%
Dew Point (°F)
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Dew Point (°C) —
Absolute Humidity —
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°F
%
Dew Point (°F)
—
Dew Point (°C) —
Absolute Humidity (g/m³) —
Actual Vapor Pressure (hPa) —
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°F
%
ft
Core Results
Dew Point (°F) —
Dew Point (°C) —
Wet Bulb Temperature (°F) —
Heat Index (°F) —
Humidity Properties
Absolute Humidity (g/m³) —
Saturation Vapor Pressure (hPa) —
Actual Vapor Pressure (hPa) —
Mixing Ratio (g/kg) —
Additional
Frost Point (°F, if <32) —
Enthalpy (kJ/kg dry air) —
How to Use This Calculator
- Enter the air temperature in °F.
- Enter the relative humidity as a percentage (0–100%).
- The calculator shows dew point in °F and °C, plus absolute humidity.
Formula
Magnus formula: γ = ln(RH/100) + (b×Tc)/(c+Tc)
Dew point °C = (c × γ) / (b − γ), where b = 17.625, c = 243.04
Example
Example: 85°F (29.4°C) air, 70% RH → Dew point ≈ 74°F (23.3°C) — muggy/uncomfortable.
Frequently Asked Questions
- The dew point is the temperature at which air becomes saturated with moisture, causing water to condense. It is a direct measure of absolute humidity in the air.
- Using the Magnus formula: γ = ln(RH/100) + (b×T)/(c+T), then dew point = (c×γ)/(b−γ), where b = 17.625 and c = 243.04°C.
- Below 55°F (13°C) feels dry, 55–65°F (13–18°C) is comfortable, 65–70°F (18–21°C) is muggy, and above 70°F (21°C) is oppressive and uncomfortable.
- Absolute humidity is the mass of water vapor per cubic meter of air (g/m³), independent of temperature. It differs from relative humidity, which is a percentage of saturation.
- No — the dew point can never exceed the air temperature. When they are equal, relative humidity is 100% and fog or condensation forms.