Dew point is the temperature at which air must be cooled for water vapor to condense into liquid water. When air temperature equals the dew point, relative humidity reaches 100%.

What is a comfortable dew point?

Dew points below 60°F (16°C) feel comfortable. Between 60–65°F it starts feeling slightly humid. Above 70°F (21°C) feels oppressive to most people.

How is dew point different from humidity?

Relative humidity is relative to how much moisture the air can hold at a given temperature. Dew point is an absolute measure of moisture content — a fixed dew point temperature means the same amount of water vapor regardless of air temperature.

What formula does this calculator use?

The Magnus formula (August–Roche–Magnus approximation) with constants a = 17.625 and b = 243.04°C, which is the standard meteorological method.

Dew Point Calculator

Air Temperature (°F)

Relative Humidity (%)

What Is Dew Point?

The dew point is the temperature at which air must be cooled — at constant pressure — for water vapor to condense into liquid water (dew). When the air temperature equals the dew point, the relative humidity reaches 100% and condensation begins on surfaces. On a humid summer day you can see this as moisture on a cold glass or morning dew on grass.

Dew point is a more reliable indicator of how humid the air feels than relative humidity alone. Relative humidity is relative to the temperature; the same amount of moisture in the air gives a different RH reading depending on how hot it is. Dew point is absolute: it measures the actual moisture content of the air.

This calculator uses the Magnus formula (August–Roche–Magnus approximation), the standard method used by meteorologists, with coefficients from Alduchov and Eskridge (1996).

Dew Point vs. Relative Humidity

Relative humidity (RH) measures how much water vapor is in the air relative to the maximum the air can hold at that temperature. RH of 100% means the air is saturated; RH of 50% means the air holds half the maximum moisture it could. On a cold day, RH can be 80% yet the air feels dry because cold air simply holds less moisture.

Dew point cuts through this: a dew point of 60°F (15°C) contains the same moisture no matter whether the air temperature is 70°F or 90°F. Forecasters and HVAC engineers prefer dew point for this reason.

Dew Point Comfort Scale

Dew Point	How It Feels
Below 50°F (10°C)	Dry, very comfortable
50–60°F (10–16°C)	Comfortable
60–65°F (16–18°C)	Slightly humid — most people notice
65–70°F (18–21°C)	Humid — uncomfortable for many
70–75°F (21–24°C)	Very humid — oppressive
Above 75°F (24°C)	Extremely humid — potentially dangerous

The Magnus Formula

This calculator uses the Magnus formula to compute dew point:

α = (a × T) / (b + T) + ln(RH / 100)

Td = (b × α) / (a − α)

where a = 17.625, b = 243.04°C, T = air temperature (°C), RH = relative humidity (%)

To reverse-calculate relative humidity from a known dew point, the formula is algebraically rearranged: RH = 100 × exp((a × Td)/(b + Td) − (a × T)/(b + T)).

Practical Uses of Dew Point

Aviation: Pilots use the temperature–dew point spread to estimate cloud base height. A spread of about 4.4°F (2.5°C) corresponds to a cloud base roughly 1,000 feet above the surface.
HVAC & building science: Knowing the dew point helps engineers size dehumidifiers, prevent condensation on ductwork, and maintain comfortable indoor conditions.
Agriculture: A dew point above the soil temperature indicates overnight dew, which affects irrigation scheduling and frost prediction.
Health & safety: Very high dew points combined with high temperatures amplify heat stress and can be life-threatening for outdoor workers or athletes.
Electronics: Data centers control dew point to prevent condensation on circuit boards, typically targeting 41–59°F (5–15°C).

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