About

This tool addresses a critical need for meteorologists, HVAC engineers, and outdoor enthusiasts who require precise atmospheric data. While simple thermometers measure air temperature, they fail to account for moisture content, which dictates the actual comfort level and condensation risks. Accurate dew point calculation is essential for preventing mold in construction, optimizing crop growth in agriculture, and predicting heat stress in athletes.

The calculator utilizes the Magnus formula to determine the temperature at which water vapor saturation occurs. Unlike standard tools, this utility includes a reverse calculation mode to derive relative humidity from a known dew point and a dynamic comfort scale that correlates physical data with human physiological response. This ensures users can translate abstract numbers into actionable safety measures for work or recreation.

Formulas

The calculation relies on the Magnus approximation, a standard in atmospheric physics for the saturation vapor pressure of water.

T_dp ≈ c ⋅ γ(T, RH)b − γ(T, RH)

Where the auxiliary function γ is defined as:

γ(T, RH) = ln(RH100) + b ⋅ Tc + T

Constants utilized (Sonntag, 1990): a = 6.112 hPa, b = 17.62, c = 243.12 °C.

Reference Data

Dew Point Range (°C)	Dew Point Range (°F)	Human Perception	Condensation Risk
< 10°C	< 50°F	A bit dry for some	Low
10°C − 12°C	50°F − 55°F	Very Comfortable	None
13°C − 16°C	55°F − 60°F	Comfortable	Minimal
16°C − 18°C	60°F − 65°F	Sticky / Humid	Moderate
18°C − 21°C	65°F − 70°F	Muggy / Uncomfortable	High (on cold surfaces)
21°C − 24°C	70°F − 75°F	Oppressive	Very High
≥ 24°C	≥ 75°F	Extreme / Dangerous	Severe

Frequently Asked Questions

Relative Humidity (RH) is relative to temperature. Cold air with 90% RH feels dry, while hot air with 50% RH can feel oppressive. Dew point provides an absolute measure of the moisture in the air. If the dew point is high, it will feel humid regardless of the air temperature.

Mold growth risk typically increases when surface temperatures drop below the dew point, causing condensation. In general, indoor dew points maintained below 15°C (59°F) significantly reduce mold risks.

No. The dew point can never exceed the air temperature. If the air cools to the dew point, the air becomes saturated (100% RH), and fog or dew forms. If it cools further, water vapor condenses out, keeping the dew point equal to the temperature.

The Magnus formula used here is standard for sea level and moderate altitudes. At very high altitudes, pressure changes affect the boiling point and vapor pressure slightly, but for general meteorological and HVAC purposes, this approximation remains highly accurate.