Dew Point Calculator
Dew point from temperature and humidity.
Enter your values
Enter the air temperature in °C.
Enter the relative humidity in %.
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
- 18.19 °C
- In Fahrenheit
- 64.74 °F
- Comfort level
- Humid
- Spread from air temp
- 5.81 °C
- Fog likely if temp falls to
- 18.2 °C
Working
- 1α = ln(70/100) + (17.625 × 24)/(243.04 + 24) = 1.2274
Quick answer
Dew point is the temperature at which air becomes saturated; above 20°C (68°F) most people find the air oppressive.
Td = (b·α) ÷ (a − α), α = ln(RH/100) + aT/(b+T)
At a glance
| What it does | Dew point from temperature and humidity. |
|---|---|
| Category | Weather |
| Inputs needed | Air temperature, Relative humidity |
| Main output | Dew point |
| Formula | Td = (b·α) ÷ (a − α), α = ln(RH/100) + aT/(b+T) |
| Cost | Free — no sign-up, no download |
How to use the Dew Point Calculator
- 1Enter the air temperature in Celsius.
- 2Enter relative humidity.
- 3Read the dew point and comfort level.
Inputs explained
- Air temperature(°C)
- Enter the air temperature in °C.
- Relative humidity(%)
- Enter the relative humidity in %.
Worked example
Using the values the calculator loads with:
Inputs
- Air temperature24 °C
- Relative humidity70 %
Results
- Dew point18.19 °C
- In Fahrenheit64.74 °F
- Comfort levelHumid
- Spread from air temp5.81 °C
- Fog likely if temp falls to18.2 °C
- α = ln(70/100) + (17.625 × 24)/(243.04 + 24) = 1.2274
Frequently asked questions
Why is dew point better than humidity?
Relative humidity depends on temperature; dew point is an absolute measure of moisture, so 20°C dew point feels muggy anywhere.
When does condensation form?
When a surface is at or below the dew point — that's why cold glasses sweat and windows fog.
What do I need to enter into the Dew Point Calculator?
Just 2 values: air temperature, relative humidity. 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; above 20°C (68°F) most people find the air oppressive. It applies the formula Td = (b·α) ÷ (a − α), α = ln(RH/100) + aT/(b+T) 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.