Dew Point Calculator
Free, accurate, and fully in-browser.
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What is Dew Point Calculator?
A dew point calculator converts air temperature and relative humidity into the dew point — the temperature at which the air becomes saturated and condensation starts. It uses the Magnus-Tetens approximation with WMO coefficients, the same relationship meteorological services rely on, and also reports absolute humidity in g/m³, actual vapor pressure in hPa, and a comfort classification. The reverse mode derives relative humidity from a known dew point.
Key Benefits
- Instant dew point from temperature and humidity with no psychrometric chart
- Absolute humidity and vapor pressure reported alongside the dew point
- Comfort scale makes mugginess comparable across days, cities, and seasons
- Bidirectional: dew point to relative humidity in one click
- Runs entirely in the browser — free, offline, and private
Common Use Cases
- •Predicting condensation on pipes, windows, camera lenses, and server hardware
- •Checking whether greenhouse, warehouse, or storage humidity is in a safe range
- •Planning outdoor workouts, events, and worksites around muggy conditions
- •Comparing humidity in weather forecasts between destinations and seasons
- •Validating HVAC and dehumidifier performance against a target dew point
How to Use the Dew Point Calculator
- Enter the air temperature: Type the dry-bulb air temperature and choose Celsius or Fahrenheit.
- Add relative humidity: Enter the relative humidity percentage from your sensor, weather station, or forecast.
- Calculate and review: Press Calculate to see the dew point, absolute humidity, vapor pressure, and the comfort classification.
- Copy or reverse the calculation: Copy the results as text, or switch modes to go from a known dew point back to relative humidity.
Key Features
- Bidirectional: temperature + RH → dew point, or temperature + dew point → RH
- Magnus-Tetens formula with WMO coefficients (valid ≈ −45 °C to +60 °C)
- Also reports absolute humidity (g/m³) and actual vapor pressure (hPa)
- Comfort scale from dry to severely high with a reference table
- Celsius and Fahrenheit with one-tap copyable results
Frequently Asked Questions
What is dew point in simple terms?
Dew point is the temperature at which air becomes fully saturated with water vapor and condensation begins. Cool a surface below the dew point and water will form on it — that is how dew, fog, and sweating cold drinks appear.
Why is dew point better than relative humidity for comfort?
Relative humidity depends on the current air temperature, so the same moisture level reads as 70% in the cool morning and 45% in the afternoon. Dew point measures the actual water content of the air, so a 21 °C dew point feels just as muggy at any hour.
How accurate is the Magnus-Tetens formula?
With the WMO coefficients used here (A = 17.62, B = 243.12), the approximation stays within about 0.1 °C of the exact calculation for temperatures between roughly −45 °C and +60 °C — far tighter than typical sensor accuracy.
Is any data sent to a server?
No. Every calculation runs locally in your browser with plain math — nothing is uploaded, logged, or stored, and the page keeps working offline once loaded.