Dew Point Calculator (Temperature & Humidity)
Find the dew point from air temperature and relative humidity — the temperature at which moisture condenses, and the best single gauge of how muggy it feels.
Calculator
At 77 °F and 60% RH the dew point is 62.1 °F (16.7 °C) — a bit humid. Below ~55 °F feels dry; above ~65 °F feels muggy.
The dew point is the temperature to which air must be cooled for its water vapor to start condensing. Unlike relative humidity — which swings with temperature and can mislead — the dew point is an absolute measure of how much moisture is actually in the air, and it tracks comfort closely. A dew point below about 55 °F feels dry and pleasant; above 65 °F feels sticky; above 70 °F is oppressive. This tool computes it from the two numbers your thermostat or a cheap hygrometer already gives you.
Dew point also explains condensation problems: window sweating, damp ductwork and mold all start where a surface is at or below the dew point. Knowing it helps you decide whether the fix is a dehumidifier, more ventilation, or better air conditioning.
Formula
Using the Magnus approximation with T in °C:
γ = ln(RH ÷ 100) + 17.625 · T ÷ (243.04 + T)
Td = 243.04 · γ ÷ (17.625 − γ)
The tool converts your Fahrenheit input to Celsius, applies the formula, then converts the dew point back to Fahrenheit (°F = °C × 9/5 + 32). The Magnus constants 17.625 and 243.04 °C are the standard fit over normal ambient temperatures.
Worked example
At 77 °F (25 °C) and 60% relative humidity:
γ = ln(0.60) + 17.625 × 25 ÷ (243.04 + 25) = −0.5108 + 1.6438 = 1.1330Td = 243.04 × 1.1330 ÷ (17.625 − 1.1330) ≈ 16.7 °C
Converting back: 16.7 × 9/5 + 32 ≈ 62.1 °F. A dew point of about 62 °F is in the “a bit humid” range — noticeably muggy but not oppressive. Drop the humidity or the temperature and the dew point falls with it. Cross-check the felt temperature with the heat index tool.
Why dew point beats relative humidity
Relative humidity is a ratio: the same 50% RH feels utterly different at 60 °F than at 90 °F, because warm air holds far more water. Dew point cuts through that — it is the actual moisture content expressed as a temperature, so a 65 °F dew point is muggy whether the thermometer reads 75 °F or 95 °F. Meteorologists and HVAC pros lean on it for exactly this reason.
For the home, the practical rule is that surfaces colder than the dew point will collect condensation. Single-pane windows sweating in winter, cold-water pipes dripping in summer, or a mold ring on an exterior wall all mean that surface is below the current dew point — either warm the surface (insulation) or lower the indoor dew point (dehumidify or ventilate). Size a dehumidifier with the dehumidifier tool.
Dew point also frames the two seasonal comfort problems. In summer, an air conditioner cools and dehumidifies as warm indoor air passes the cold coil, so a system that is oversized or short-cycles cools the thermostat quickly but leaves the dew point high and the house clammy — one more reason right-sizing matters. In winter, indoor air with a dew point above the temperature of a single-pane window or an uninsulated wall corner will condense there and eventually grow mold. Aiming for an indoor dew point in the low-to-mid 50s °F keeps most homes both comfortable and condensation-free.
Reference table
Dew-point comfort bands:
| Dew point | How it feels |
|---|---|
| ≤ 55 °F | Dry / comfortable |
| 55–60 °F | Comfortable |
| 60–65 °F | A bit humid |
| 65–70 °F | Muggy |
| ≥ 70 °F | Oppressive |
General comfort guidance; individual tolerance varies.