Dew Point Calculator
Calculate dew point temperature from air temperature and humidity.
Calculate the dew point temperature — the point at which air becomes saturated with moisture — from air temperature and relative humidity.
How Dew Point Calculator Works
Dew point is the temperature air would need to cool to (at constant pressure and moisture content) for it to become fully saturated and start condensing as dew, fog, or frost. Unlike relative humidity, which changes with temperature, dew point is a more direct measure of how much moisture is actually in the air.
The calculator uses the Magnus formula, a well-established approximation: it first computes an intermediate value α = (17.27 × T) ÷ (237.7 + T) + ln(RH ÷ 100), then solves for dew point as (237.7 × α) ÷ (17.27 − α), where T is air temperature in °C and RH is relative humidity as a percentage.
A higher dew point means more actual moisture in the air and generally more oppressive, muggy conditions — it is considered a more reliable "mugginess" indicator than relative humidity alone.
See It In Action
Who Uses Dew Point Calculator and Why
- Checking how muggy the air will actually feel, since dew point is a more consistent indicator than relative humidity alone.
- Predicting the likelihood of morning fog or frost based on how close the current temperature is to the dew point.
- Comparing humidity conditions across two different days or locations at different temperatures, where relative humidity alone isn't a fair comparison.
- Understanding a weather forecast's dew point figure and what it means for outdoor comfort.
Mistakes to Avoid
- Comparing relative humidity readings directly across two days with very different temperatures to judge mugginess — relative humidity depends heavily on current temperature, so the same moisture level reads differently depending on how warm it is; dew point avoids this issue.
- Entering temperature in °F when the underlying Magnus formula expects °C, or misreading a Celsius result as Fahrenheit.
- Expecting a dew point result higher than the air temperature — that's not physically possible, since dew point equals air temperature only at 100% relative humidity (full saturation) and can't exceed it.
Tips for Best Results
- Use dew point rather than relative humidity when comparing how muggy two different days feel, since it reflects actual moisture content rather than a temperature-relative percentage.
- A dew point below 60°F (15.5°C) generally feels comfortable, 60-70°F (15.5-21°C) feels increasingly humid, and above 70°F (21°C) feels oppressive to most people.
Fixing Common Problems
My dew point result is higher than the air temperature I entered. — This isn't physically possible and usually indicates a units mix-up (like entering Fahrenheit where Celsius was expected) — dew point can equal air temperature at full saturation but never exceed it.
Terms Explained
Dew point: The temperature air must cool to (at constant pressure and moisture) to become fully saturated and begin condensing as dew, fog, or frost.
Magnus formula: A well-established approximation formula used to calculate dew point from air temperature and relative humidity.