At 75 °F and 60% relative humidity the dew point is about 60.2 °F, which most people find humid. Add a surface temperature to check whether a window, pipe or wall will sweat.
How the dew point calculator works
DewPointCalc uses the Magnus formula with the Alduchov and Eskridge constants a = 17.625 and b = 243.04 °C. With the air temperature T in °C and relative humidity RH, it computes γ = ln(RH/100) + a·T/(b + T), and the dew point is b·γ/(a − γ). Going the other way, RH = 100·exp(a·Td/(b + Td) − a·T/(b + T)). Absolute humidity comes from the saturation vapour pressure, 6.112·exp(17.67·T/(T + 243.5)) hPa, times RH × 2.1674 divided by the temperature in kelvin. A surface at or below the dew point gets condensation; for painting, keep it at least 5 °F (3 °C) above.
Dew point comfort chart
| Dew point | Feels | Notes |
|---|---|---|
| Below 40 °F (4 °C) | Very dry | dry skin and static are likely, especially indoors |
| 40–54 °F | Comfortable | pleasant for most people |
| 55–59 °F | Slightly humid | still comfortable for most, a little sticky for some |
| 60–64 °F | Humid | sticky; most people notice the moisture |
| 65–69 °F | Muggy | uncomfortable, sweat evaporates slowly |
| 70–74 °F | Oppressive | very uncomfortable; take care with exercise |
| 75 °F (24 °C) and up | Miserable | dangerous for strenuous activity |
Dew point at 70 °F by humidity
| Relative humidity | Dew point |
|---|---|
| 20% | 27.1 °F |
| 30% | 37.1 °F |
| 40% | 44.6 °F |
| 50% | 50.5 °F |
| 60% | 55.5 °F |
| 70% | 59.8 °F |
| 80% | 63.5 °F |
| 90% | 66.9 °F |
Frequently asked questions
What is the dew point?
The temperature the air would have to cool to, at the same moisture content, to reach 100% relative humidity. Below it, water condenses.
Is dew point better than humidity for comfort?
Yes. Relative humidity changes with temperature, while the dew point measures the actual moisture, so it tracks how sticky it feels.
Can the dew point be higher than the temperature?
No. At 100% humidity they are equal; the dew point can never be above the air temperature.
Is DewPointCalc free?
Yes, with no sign-up or ads, and your readings stay in your browser.
How accurate is the result?
The formula is accurate to about 0.4 °C; most home hygrometers are only accurate to 2–5% RH, which matters more.