Dew Point Calculator

Dew point is the temperature air would have to cool to, at constant pressure and moisture content, for it to become fully saturated (100% relative humidity) and start condensing. It's calculated here with the Magnus-Tetens approximation in its Sonntag (1990) form: γ(T, RH) = (β×T) ÷ (λ+T) + ln(RH ÷ 100), then dew point Td = (λ×γ) ÷ (β−γ), using the constants β = 17.62 and λ = 243.12°C. This form is valid for air temperatures from −45°C to 60°C, which is why the calculator rejects inputs outside that range rather than silently returning an inaccurate result.

At exactly 100% relative humidity, the ln(RH ÷ 100) term is ln(1) = 0, and the formula reduces algebraically to exactly Td = T — the dew point and air temperature coincide, which makes physical sense since fully saturated air is already at its own dew point.

The further apart the dew point and air temperature sit (the 'dew point depression' shown alongside the result), the drier the air actually is at that temperature — relative humidity alone can be misleading since the same percentage means very different amounts of moisture in warm air versus cold air, while dew point tracks the air's actual moisture content directly.