With Td = (b * α(T,RH)) / (a – α(T,RH)) formula, our dew point calculator effortlessly determines the temperature at which water vapor in the air begins to condense into liquid water, forming dew.
The air temperature is 25°C (77°F) with a relative humidity of 60%. Using dew point calculator, we find that the dew point is approximately 16.7°C (62.1°F). This means that if the air temperature drops to 16.7°C, water vapor will start condensing, potentially forming dew on surfaces.
Dew Point Calculator
| Temperature (°C) | Relative Humidity (%) | Dew Point (°C) | Comfort Level |
|---|---|---|---|
| 10 | 30 | -1.2 | Comfortable |
| 15 | 40 | 3.0 | Comfortable |
| 20 | 50 | 9.3 | Comfortable |
| 22 | 55 | 11.6 | Comfortable |
| 25 | 60 | 16.7 | Slightly humid |
| 27 | 65 | 18.5 | Slightly uncomfortable |
| 30 | 70 | 23.9 | Uncomfortable |
| 32 | 75 | 26.2 | Quite uncomfortable |
| 35 | 80 | 29.0 | Extremely uncomfortable |
| 28 | 85 | 25.5 | Uncomfortable |
| 18 | 90 | 17.0 | Comfortable |
| 12 | 95 | 11.5 | Comfortable |
| 40 | 50 | 24.0 | Uncomfortable |
| 38 | 60 | 26.0 | Quite uncomfortable |
| 36 | 70 | 27.5 | Extremely uncomfortable |
| 34 | 80 | 29.0 | Extremely uncomfortable |
| 33 | 90 | 31.0 | Extremely uncomfortable |
| -5 | 20 | -8.0 | Comfortable |
Dew Point Formula
The Magnus-Tetens formula is used to calculate dew point:
Td = (b * α(T,RH)) / (a - α(T,RH))Where:
- Td is the dew point temperature
- T is the air temperature
- RH is the relative humidity (expressed as a decimal)
- a and b are constants (a = 17.27, b = 237.7°C)
- α(T,RH) = ((a * T) / (b + T)) + ln(RH)
Given: T = 20°C, RH = 65% (0.65)
Calculate α(T,RH): α(20,0.65) = ((17.27 * 20) / (237.7 + 20)) + ln(0.65) ≈ 1.9751
Apply the Magnus-Tetens formula: Td = (237.7 * 1.9751) / (17.27 – 1.9751) ≈ 13.2°C
The dew point for air at 20°C with 65% relative humidity is approximately 13.2°C.
How to Calculate Dewpoint?
Calculating dew point involves these steps:
Gather necessary data: air temperature and relative humidity
Apply the dew point formula (e.g., Magnus-Tetens)
Solve the equation to find the dew point temperature
Given: Temperature = 30°C, Relative Humidity = 70%Using the Magnus-Tetens formula:
- α(30,0.70) = ((17.27 * 30) / (237.7 + 30)) + ln(0.70) ≈ 2.7681
- Td = (237.7 * 2.7681) / (17.27 – 2.7681) ≈ 23.9°C
The dew point in this scenario is approximately 23.9°C.
How to calculate dew point without relative humidity?
- Wet-bulb and dry-bulb temperatures: Employ a psychrometer to measure both temperatures, then use psychrometric charts or calculators to determine the dew point.
- Absolute humidity: If you know the absolute humidity (mass of water vapor per unit volume of air), you can calculate dew point using specialized formulas or tables.
Using wet-bulb and dry-bulb temperatures:
- Dry-bulb temperature: 25°C
- Wet-bulb temperature: 20°C
Using a psychrometric chart, we can estimate the dew point to be around 17°C.
What is an Uncomfortable Dew Point?
Dew points above 18°C (65°F) start to feel uncomfortable, with higher values causing increasing discomfort:
- 18-21°C (65-70°F): Slightly uncomfortable
- 21-24°C (70-75°F): Quite uncomfortable
- Above 24°C (75°F): Extremely uncomfortable
If the temperature is 30°C (86°F) with a dew point of 23°C (73.4°F), most people would find this combination quite uncomfortable due to the high moisture content in the air, which hinders the body’s natural cooling process through perspiration.
What is the dew point if the humidity is 65?
Given: Temperature = 25°C, Relative Humidity = 65%
Using the Magnus-Tetens formula:
α(25,0.65) = ((17.27 * 25) / (237.7 + 25)) + ln(0.65) ≈ 2.4076Td = (237.7 * 2.4076) / (17.27 - 2.4076) ≈ 17.9°CAt 25°C with 65% humidity, the dew point is approximately 17.9°C (64.2°F).
What is the ideal dew point?
The ideal dew point for human comfort typically falls between 10°C and 16°C (50°F to 60°F). This range provides a pleasant balance of moisture in the air:
- It’s neither too dry, which can cause discomfort in breathing and dry skin
- Nor too humid, which can lead to discomfort and excessive perspiration
A room at 22°C (71.6°F) with a dew point of 12°C (53.6°F) would feel comfortable for most people, allowing for efficient evaporative cooling of the body without feeling excessively dry or damp.
References
- National Weather Service. “Dew Point Calculator.” https://www.weather.gov/epz/wxcalc_dewpoint
- American Meteorological Society. “Glossary of Meteorology.” https://glossary.ametsoc.org/wiki/Dew_point
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