Dew Point Comfort Zone
Dew point from air temperature and relative humidity by the Magnus formula, with the tool’s own comfort bands from Dry to Very oppressive. How it works
Use the Dew Point Comfort Zone
About the Dew Point Comfort Zone
At 75 °F and 60% relative humidity the dew point is 60.2 °F (15.6 °C), which this tool labels Comfortable. It uses the Magnus formula, and at 100% humidity the dew point equals the air temperature. Below 0 °C the figure it shows is the frost point. The same air holds 12.9 g of water per cubic metre at a vapor pressure of 17.7 hPa, which the tool also shows.
Dew point in °F by air temperature and relative humidity
| Air temperature | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|
| 60 °F | 35.6°F | 41.3°F | 46.1°F | 50.2°F | 53.8°F | 57.1°F |
| 70 °F | 44.6°F | 50.5°F | 55.5°F | 59.8°F | 63.5°F | 66.9°F |
| 75 °F | 49.0°F | 55.1°F | 60.2°F | 64.5°F | 68.4°F | 71.9°F |
| 80 °F | 53.5°F | 59.7°F | 64.9°F | 69.3°F | 73.3°F | 76.8°F |
| 85 °F | 58.0°F | 64.3°F | 69.6°F | 74.1°F | 78.1°F | 81.7°F |
| 90 °F | 62.4°F | 68.9°F | 74.2°F | 78.9°F | 83.0°F | 86.7°F |
Computed with the Magnus formula the page uses, shown to one decimal as the page shows it.
The tool’s comfort bands
| Band | Dew point |
|---|---|
| Dry | below 55 °F |
| Comfortable | 55 °F up to 65 °F |
| Warm | 65 °F up to 70 °F |
| Muggy | 70 °F up to 75 °F |
| Oppressive | 75 °F up to 80 °F |
| Very oppressive | 80 °F and above |
These are this tool’s own bands. Published sources draw the lines at different dew points, so another site can label the same air differently.
How to use this tool
- Pick °F or °C. Switching converts the temperature you typed, so the same air is shown in the new unit.
- Enter the air temperature and the relative humidity.
- Read the dew point, the comfort band, the vapor pressure in hPa, the absolute humidity in g/m³ and the notes for outdoor effort and indoor humidity. A condensation note appears only when the air is within 15 °F of its dew point.
Frequently asked questions
- How do you calculate dew point from temperature and humidity?
- With the Magnus formula: γ = ln(RH ÷ 100) + b·T ÷ (c + T), then dew point = c·γ ÷ (b − γ), with T in °C. The tool uses b = 17.62 and c = 243.12 at or above 0 °C. At 75 °F and 60% it gives 60.2 °F. The same b and c give the vapor pressure, e = RH ÷ 100 × 6.112 × exp(b·T ÷ (c + T)) hPa, and the absolute humidity, 216.7 × e ÷ (T + 273.15) g/m³: 11.7 hPa and 8.6 g/m³ at 20 °C and 50%. Bolton’s b = 17.67 and c = 243.5, which some sites use, give about 0.02 hPa more for that air.
- What dew point is comfortable?
- Wikipedia’s dew point article gives the usual guide for temperate climates: many people start to feel uncomfortable above 15 °C (59 °F), almost everyone feels sticky by 20 °C (68 °F), and most find dew points above 21 °C (70 °F) oppressive. This tool’s own bands sit higher: it labels 55 to under 65 °F Comfortable, 70 to under 75 °F Muggy and 75 to under 80 °F Oppressive, so a 72 °F dew point that it calls Muggy is oppressive on that guide.
- What is the dew point at 100% relative humidity?
- It equals the air temperature. At 30 °F and 100% the tool shows a dew point of 30.0 °F.
- Can I enter the temperature in Celsius?
- Yes. Choose °C and type the temperature: 24 °C at 50% gives a dew point of 12.9 °C (55.3 °F). Switching units converts what you typed, so 75 °F becomes 23.9 °C.
- Is dew point the same as heat index?
- No. The dew point comes from air temperature and humidity only. It does not measure heat stress, so check the heat index in a local forecast.
- Does it work below freezing?
- Yes, down to −50 °F, but below 0 °C it gives the frost point, the temperature at which the moisture would deposit as frost. It switches to the Magnus constants for saturation over ice that the UK National Physical Laboratory gives, b = 22.46 and c = 272.62. At −5 °C and 80% the tool shows −7.6 °C, where the over-water constants give −7.9 °C, and the result steps by about 0.36 °C as the air crosses 0 °C.
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