Dew Point Calculator
Calculate dew point from temperature and relative humidity, or reverse it back to humidity. Includes comfort scale and Magnus formula reference.
Definition: The dew point is the temperature at which air becomes saturated when cooled at constant pressure and constant moisture content. This tool applies the Magnus-Tetens formula with coefficients a = 17.27 and b = 237.7 °C.
Temperature (°C): −40 ≤ T ≤ 60; Relative Humidity (%): 0 < RH ≤ 100; Dew Point (°C): −237.7 < Td ≤ T.
Dew Point Comfort Scale
- Below 10 °CDry and crisp
- 10–16 °CComfortable
- 16–20 °CNoticeably humid
- 20–24 °CMuggy and sticky
- Above 24 °COppressive
Why Dew Point?
- Dew point measures the actual moisture in the air
- It does not change when temperature changes
- Dew point above 20 °C feels muggy for most people
How to Use the Dew Point Calculator
Pick a Direction
Choose humidity to dew point, or the reverse
Enter Temperature
Input the current air temperature in Celsius
Enter the Known Value
Type relative humidity or dew point as available
Read the Results
See the conversion, vapor pressure, and comfort
The Magnus Formula & Dew Point Chart
Td = (237.7 · γ) / (17.27 − γ)
Temperature (°C): −40 ≤ T ≤ 60; Relative Humidity (%): 0 < RH ≤ 100.
RH = 100 × exp((17.27 × Td)/(237.7 + Td) − (17.27 × T)/(237.7 + T))
Worked Examples
Temperature (°C): 25; Relative Humidity (%): 50 → Dew Point (°C): 13.8.
Relative Humidity (%): 100 → Td = T.
| Dew Point (°C) | RH at 20 °C | RH at 25 °C | RH at 30 °C | Feels Like |
|---|---|---|---|---|
| 0 | 26% | 19% | 14% | Dry |
| 5 | 37% | 28% | 21% | Dry |
| 10 | 53% | 39% | 29% | Comfortable |
| 14 | 68% | 51% | 38% | Comfortable |
| 18 | 88% | 65% | 49% | Humid |
| 22 | — | 83% | 62% | Muggy |
| 26 | — | — | 79% | Oppressive |
Frequently Asked Questions
How is dew point calculated?
Dew point is calculated from air temperature and relative humidity using the Magnus-Tetens formula: first compute γ = ln(RH/100) + (17.27 × T)/(237.7 + T), then Td = (237.7 × γ)/(17.27 − γ). This calculator applies the formula instantly as you type, accurate to about 0.35 °C between −40 °C and +50 °C.
What is a good dew point for indoors?
For indoor comfort, aim for a dew point between about 7 °C and 16 °C, which corresponds to 30–60% relative humidity at typical room temperatures. Below a 7 °C dew point the air feels dry (increasing static and dry skin); above 16 °C it feels humid and condensation risk on cold surfaces rises.
Why is dew point better than relative humidity?
Relative humidity depends on temperature: the same moist air shows 50% RH at 20 °C but only 25% RH at 30 °C. Dew point measures the actual moisture content, so it stays constant as temperature changes. That is why dew point is the standard way to compare humidity across different times and places.
At what dew point does it feel muggy?
Most people notice mugginess once the dew point exceeds 18–20 °C. A dew point above 24 °C feels oppressive and can be dangerous during physical activity, because sweat evaporates poorly. Below 10 °C the air feels crisp and dry regardless of the relative humidity reading.
Can I calculate dew point from wet-bulb temperature?
Yes — this page accepts air temperature plus either relative humidity or dew point. If you only have a wet-bulb reading, convert it first: e ≈ e_w − 0.00066 × (1 + 0.00115 × Tw) × P × (T − Tw), where e_w is saturation vapor pressure at the wet-bulb temperature. Then RH = 100 × e / es and enter the result here.
Convert between different units of measurement