Dew Point Calculator
Last updated: June 2026 · Free · No sign-up required
Enter values above and click Calculate to see your result instantly.
Quick reference
| Dew point | How it feels |
|---|---|
| Below 10 °C (50 °F) | Dry, comfortable |
| 10 – 16 °C (50–60 °F) | Comfortable |
| 16 – 18 °C (60–65 °F) | Getting sticky |
| 18 – 21 °C (65–70 °F) | Humid, uncomfortable |
| Above 21 °C (70 °F) | Oppressive, muggy |
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Responsive design tested down to a 320px-wide phone screen. The input fields use native number/date keyboards on iOS and Android, the calculate button is thumb-sized, and the result still reads big and bold on the smallest screen. No app to download, ever.
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Interpretation guide
| Relationship | Note |
|---|---|
| Dew point = air temp | 100% relative humidity (fog/dew likely) |
| Larger gap | Drier air, lower humidity |
| Dew point | Absolute moisture — more stable than RH |
Formula & methodology
Formula: alpha = ln(RH/100) + a*T/(b+T); Td = b*alpha/(a - alpha) with a = 17.625, b = 243.04 (°C)
How dew point is calculated
The dew point is the temperature to which air must cool for its water vapor to start condensing. It is computed from temperature and relative humidity with the Magnus-Tetens approximation.
Example
At 25 °C and 60% RH: alpha = ln(0.60) + 17.625 x 25 / (243.04 + 25) = -0.511 + 1.644 = 1.133. Td = 243.04 x 1.133 / (17.625 - 1.133) = 275.4 / 16.49 = 16.7 °C.
Unlike relative humidity, dew point is an absolute measure of moisture, so it is a better gauge of how muggy it actually feels. When dew point equals the air temperature, the air is saturated and dew, fog, or rain becomes likely.