That air holds about 8.6 g of water per cubic metre and has a dew point of about 48.7 °F.
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 difference between absolute and relative humidity?
Absolute humidity is the actual water content in g/m³; relative humidity is that amount as a percentage of the most the air could hold at its temperature.
How much water can air hold?
About 17 g/m³ at 20 °C and 30 g/m³ at 30 °C when saturated.
Why is winter air dry indoors?
Cold outdoor air holds little water; heated indoors, its relative humidity drops sharply.
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.