Enter your air temperature, dew point, and ground elevation to calculate the cloud base altitude — the height at which clouds are likely to form. The Cloud Base Calculator also estimates the cloud temperature at that altitude. Choose between Fahrenheit/feet or Celsius/meters for your preferred unit system.
Cloud Base Altitude (ASL)
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Cloud Base Height (AGL)
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Cloud Temperature
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Temperature–Dew Point Spread
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The cloud base is the lowest altitude at which visible clouds begin to form. It is determined by the point where rising air cools to its dew point temperature, causing water vapor to condense into visible cloud droplets. Pilots and meteorologists monitor cloud base height for safety and weather forecasting.
The standard formula for cloud base height above ground level (AGL) is: Cloud Base AGL = ((Temperature − Dew Point) / 4.4) × 1000 feet, or in metric: ((Temperature − Dew Point) / 10) × 1247 meters. Add your ground elevation to get the altitude above sea level (ASL).
You need three values: (1) the surface air temperature, (2) the dew point temperature at the same location, and (3) your ground elevation above sea level. All three should be measured at the same location and approximately the same time for the most accurate result.
The temperature at the cloud base can be estimated because air cools at the dry adiabatic lapse rate as it rises. In imperial units, the cloud temperature ≈ Surface Temperature − 5.4 × (Cloud Base AGL / 1000) °F. In metric, it is ≈ Surface Temperature − 0.984 × (Cloud Base AGL / 100) °C.
The temperature–dew point spread is simply the difference between the air temperature and the dew point. A smaller spread means the air is closer to saturation, so clouds form at lower altitudes. A spread of less than 2°C (or ~4°F) typically indicates fog or very low clouds.
This formula is most accurate for convective cumulus clouds, which form as warm, moist air rises from the surface and cools to its dew point. It is less applicable to stratus or orographic clouds, which form through different mechanisms such as horizontal airflow or lifting over terrain.
AGL (Above Ground Level) is the height of the cloud base measured from the ground directly below it. ASL (Above Sea Level) adds your ground elevation to that height, giving the altitude as measured from mean sea level — the standard reference used in aviation and meteorology.
The formula provides a reliable estimate for fair-weather cumulus clouds under standard atmospheric conditions. Real-world accuracy depends on how precisely you measure temperature and dew point. Atmospheric instability, frontal systems, or unusual lapse rates can cause actual cloud bases to differ from the calculated value.