Dew Point Calculator

Dew Point is calculated with the Magnus formula, a standard meteorological approximation that converts Air Temperature and Relative Humidity into the temperature at which the air would become saturated and water vapor would begin condensing. Both Air Temperature and Relative Humidity push Dew Point in the same direction — warmer air or higher humidity both raise the calculated dew point — and which one moves the result more depends on where you're starting from: Air Temperature's effect grows stronger the warmer the air already is, while Relative Humidity's effect stays comparatively steady across its range, so neither input reliably dominates the other over this calculator's full declared ranges. The Magnus coefficients used here (a = 17.27, b = 237.7) are validated for air temperatures between 0°C and 60°C; below freezing the result is still the dew point over liquid water rather than the frost point over ice, which uses a different coefficient pair, so treat sub-freezing results as approximate.

Comfort Level buckets the resulting dew point (converted to Celsius internally regardless of your selected display unit) into the standard published dew-point comfort scale: a below-freezing band where the mugginess scale simply does not apply, then seven bands from "Dry & comfortable" below 10°C up to "Severely high — heat stress risk" above 24°C (75°F); dew point, not relative humidity alone, is the figure meteorologists generally consider the more reliable indicator of how humid the air actually feels, since a given relative humidity percentage means very different things at different temperatures. Frost Risk requires more than a sub-freezing dew point: actual frost needs a surface at or below freezing, which needs the air temperature itself to fall close to the dew point, so the flag distinguishes air that is already at or below freezing, air within about 10°F of its sub-freezing dew point where overnight cooling could plausibly reach it, and the ordinary case of dry warm air with a sub-freezing dew point that poses no frost risk at all. This is a physics-based formula rather than a manufacturer-calibrated instrument reading, so it will differ slightly from a dedicated dew point sensor, and it does not account for elevation, air pressure, or local microclimate effects.