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Dew point calculator
Short answer
The dew point is the temperature air must cool to before its moisture condenses, and it tracks how muggy it feels better than relative humidity does. At 85 °F (29 °C) and 60% humidity, the dew point is about 70 °F (21 °C), which the National Weather Service describes in summer as "lots of moisture in the air, becoming oppressive".
Last reviewed 28 October 20263 published sourcesNot medical advice
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Use the air temperature and relative humidity from a weather app.
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| Air temperature | 30% RH | 50% RH | 70% RH | 90% RH |
|---|---|---|---|---|
| 60 °F (16 °C) | 29 | 41 | 50 | 57 |
| 70 °F (21 °C) | 37 | 51 | 60 | 67 |
| 80 °F (27 °C) | 46 | 60 | 69 | 77 |
| 90 °F (32 °C) | 54 | 69 | 79 | 87 |
| 100 °F (38 °C) | 63 | 78 | 88 | 97 |
| Dew point | Description |
|---|---|
| 55 °F or lower | dry and comfortable |
| 55–65 °F | becoming “sticky” with muggy evenings |
| 65 °F or higher | lots of moisture in the air, becoming oppressive |
The National Weather Service formula
The saturation vapour pressure is es = 6.11 × 10^(7.5 × T / (237.3 + T)) hPa, with T in °C, and relative humidity is the actual vapour pressure as a percentage of it (National Weather Service: vapor pressure). Solving for the dew point gives Td = 237.3 × ln(es × rh / 611) / (7.5 × ln 10 − ln(es × rh / 611)) (National Weather Service: dewpoint).
The comfort bands come from a National Weather Service office's summer guide: 55 °F or lower is dry and comfortable, 55–65 °F becomes sticky with muggy evenings, and 65 °F or higher is oppressive (National Weather Service La Crosse).
For heat stress during exercise, use the WBGT calculator or the heat index calculator.
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Common questions
What dew point is comfortable?
A National Weather Service guide for summer calls a dew point of 55 °F (13 °C) or lower dry and comfortable, 55–65 °F sticky with muggy evenings, and 65 °F (18 °C) or higher oppressive.
Why use dew point instead of humidity?
Relative humidity depends on temperature, so 50% feels very different on a cool morning and a hot afternoon. The dew point measures the actual moisture in the air, so the same dew point feels similarly muggy whatever the temperature.
How is the dew point calculated?
The National Weather Service first works out the saturation vapour pressure, es = 6.11 × 10^(7.5T / (237.3 + T)) hPa with T in °C, then the dew point as Td = 237.3 × ln(es × rh / 611) / (7.5 × ln 10 − ln(es × rh / 611)).
Sources
Figures on this page were checked against these publications on 28 October 2026.
- National Weather Service, El Paso. Weather calculator notes: Vapor Pressure. NOAA. www.weather.gov/media/epz/wxcalc/vaporPressure.pdf
- National Weather Service, El Paso. Weather calculator notes: Wet-bulb Temperature and Dewpoint Temperature from Air Temperature and Relative Humidity. NOAA. www.weather.gov/media/epz/wxcalc/wetBulbTdFromRh.pdf
- National Weather Service, La Crosse. Why dewpoint vs humidity? NOAA. www.weather.gov/arx/why_dewpoint_vs_humidity
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