Dew Point Calculator
Dew point from temperature and humidity.
Enter your values
Enter the temperature in °F.
Enter the relative humidity in %.
Enter the surface temperature in °F.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Dew point
- 57.7 °F
- In °C
- 14.3
- Surface temperature
- 58 °F
- Condensation risk
- No — surface stays dry
- Margin
- 0.3 °F
Quick answer
Dew point is the temperature at which air becomes saturated and moisture begins to condense on surfaces.
Magnus formula from temperature and RH
At a glance
| What it does | Dew point from temperature and humidity. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Temperature, Relative humidity, Surface temperature |
| Main output | Dew point |
| Formula | Magnus formula from temperature and RH |
| Cost | Free — no sign-up, no download |
How to use the Dew Point Calculator
- 1Enter room temperature and relative humidity.
- 2Enter the surface temperature of the duct, window or wall you are worried about.
- 3Insulate or dehumidify until the surface stays above dew point.
Inputs explained
- Temperature(°F)
- Enter the temperature in °F.
- Relative humidity(%)
- Enter the relative humidity in %.
- Surface temperature(°F)
- Enter the surface temperature in °F.
Worked example
Using the values the calculator loads with:
Inputs
- Temperature75 °F
- Relative humidity55 %
- Surface temperature58 °F
Results
- Dew point57.7 °F
- In °C14.3
- Surface temperature58 °F
- Condensation riskNo — surface stays dry
- Margin0.3 °F
Frequently asked questions
Why do ducts sweat?
Chilled supply duct in humid unconditioned space drops below dew point; vapour-sealed insulation fixes it.
Comfort dew point?
Below 55°F feels dry and pleasant; above 65°F feels muggy regardless of temperature.
What do I need to enter into the Dew Point Calculator?
Just 3 values: temperature, relative humidity, surface temperature. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Dew Point Calculator work out the answer?
Dew point is the temperature at which air becomes saturated and moisture begins to condense on surfaces. It applies the formula Magnus formula from temperature and RH and shows the working so you can check each step by hand.
Is the Dew Point Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.