What is the Dew Point Calculator?
Calculate dew point from air temperature and relative humidity with this free dew point calculator. Use the Magnus inversion formula to find the temperature at which air saturates, or work backward from temperature and dew point to get relative humidity. Also shows vapor pressure, absolute humidity in g/m³, comfort level, and condensation risk. Supports metric (°C) and imperial (°F). Results update instantly in your browser with no signup.
How to use the Dew Point Calculator
- Choose From Humidity (T + RH → dew point) or From Dew Point (T + Td → RH).
- Select metric (°C) or imperial (°F).
- Enter air temperature and either relative humidity or dew point.
- Review dew point, vapor pressure, absolute humidity, comfort level, and condensation notes.
- Try presets such as 20°C at 50% RH or 30°C at 70% RH for common summer conditions.
Common use cases
- Finding dew point from a weather station temperature and humidity reading
- Checking if overnight lows will reach dew point and cause fog or frost
- Estimating relative humidity when you know temperature and dew point
- Teaching how absolute humidity and vapor pressure relate to comfort
- HVAC, agriculture, and photography planning where condensation matters
Frequently asked questions
- What is dew point?
- Dew point is the temperature to which air must be cooled (at constant pressure) to become saturated with water vapor. When air temperature drops to the dew point, condensation forms as dew, fog, or clouds.
- How is dew point calculated?
- This tool uses the Magnus inversion: γ = ln(RH/100) + (17.27×T)/(237.7+T), then Td = (237.7×γ)/(17.27−γ), with T in °C. Vapor pressure uses the Magnus-Tetens saturation formula.
- What dew point feels comfortable?
- Below 10°C (50°F) feels dry; 10–16°C is comfortable for most people; 16–18°C is slightly humid; above 18°C feels muggy; above 21°C is oppressive. Forecasters often prefer dew point over relative humidity for comfort because it does not change with temperature alone.
- Can dew point be higher than air temperature?
- No under normal conditions — that would mean supersaturation. If you enter a dew point above air temperature in reverse mode, the calculator returns an error.
- How is this related to heat index?
- Both describe moisture in air. Dew point is the actual saturation temperature; heat index combines temperature and humidity into a feels-like value for hot weather. Use both tools together for a full picture of humid conditions.
