Dew point formula (Magnus)
γ = ln(RH ÷ 100) + 17.625 × T ÷ (243.04 + T)
Dew point = 243.04 × γ ÷ (17.625 − γ)
(T in °C)
Worked example
At 80 °F (26.7 °C) and 60% relative humidity, γ = ln(0.6) + 17.625 × 26.7 ÷ 269.7 = 1.232, so the dew point is 243.04 × 1.232 ÷ 16.39 ≈ 18.3 °C, or about 65 °F. That feels humid and a bit sticky.
Dew point comfort scale
| Dew point | How it feels |
|---|
| Below 50 °F (10 °C) | Dry and comfortable |
| 50–54 °F (10–12 °C) | Very comfortable |
| 55–59 °F (13–15 °C) | Comfortable |
| 60–64 °F (16–17 °C) | Slightly humid |
| 65–69 °F (18–20 °C) | Humid, a bit sticky |
| 70–74 °F (21–23 °C) | Very humid, uncomfortable |
| 75 °F (24 °C) and up | Oppressive |
Need to convert other temperatures? Use the unit converter.
Last reviewed October 2026.
Frequently asked questions
What is the dew point?
The dew point is the temperature air has to cool to for water vapor to condense into dew, fog or condensation. The closer the dew point is to the air temperature, the more humid it feels. When they match, relative humidity is 100%.
What is the difference between dew point and relative humidity?
Relative humidity is a percentage that changes with temperature during the day. Dew point measures the actual amount of moisture in the air, so it is a better guide to how muggy it feels: a 65 °F dew point feels sticky whether the air is 75 °F or 90 °F.
What dew point is comfortable?
Most people find dew points below about 55 °F (13 °C) comfortable, 60–65 °F (16–18 °C) noticeably humid and above 70 °F (21 °C) oppressive. The table on this page shows the full scale.
Which formula does this use?
It uses the Magnus formula with the Alduchov–Eskridge constants (17.625 and 243.04 °C), which is accurate to within about 0.1 °C over normal weather temperatures from −40 to 50 °C.
Why does dew point matter at home?
If a surface, such as a cold window, pipe or basement wall, is colder than the dew point, water will condense on it. Keeping indoor humidity down lowers the dew point and helps prevent condensation and mold.