Cloud Base
Calculate the altitude at which clouds form using temperature and dew point. Free online cloud base calculator with metric and imperial results, charts, and temperature spread.
About This Calculator
The Cloud Base Altitude Calculator estimates the minimum altitude above mean sea level at which clouds are likely to form. By entering the current air temperature and dew point at your location, the calculator uses the standard adiabatic lapse rate to determine the altitude at which rising air cools to its dew point temperature — the point of saturation where condensation begins and clouds form. This tool is essential for pilots, meteorologists, glider and sailplane pilots, hikers, photographers, and weather enthusiasts who need to estimate cloud height for aviation planning, outdoor activities, or weather observation.
The calculation is based on the difference between air temperature and dew point, known as the temperature spread. As air rises, it cools at the dry adiabatic lapse rate of approximately 9.8°C per 1000 meters (5.4°F per 1000 feet), while the dew point decreases at a slower rate of about 1.8°C per 1000 meters (1.0°F per 1000 feet). The spread therefore converges at a rate of roughly 8°C per 1000 meters, meaning the temperature and dew point meet after every 125 meters (410 feet) of ascent per degree Celsius of spread. The formula is: Cloud Base (m) = Temperature Spread (°C) × 125 + Elevation (m). In imperial units: Cloud Base (ft) = (Temperature (°F) − Dew Point (°F)) / 4.4 × 1000 + Elevation (ft). The cloud temperature is then computed by applying the dry adiabatic lapse rate from the surface to the cloud base altitude.
Regional Notes: This calculator works universally across all regions. In the United States and United Kingdom, aviation weather reports (METARs) often report cloud base in feet above ground level (AGL), and the imperial formula is standard among general aviation pilots. In India and most other countries, cloud base is typically reported in meters above mean sea level (AMSL) for aviation and meteorological purposes. The calculator provides both metric and imperial results so it serves users worldwide. For best accuracy, use temperature and dew point measurements taken at the same location and time — ideally from the nearest weather station or a handheld weather meter.
Frequently Asked Questions
How do you calculate cloud base altitude?
Cloud base altitude is calculated using the formula: cloud base (m) = (temperature - dew point) × 125 + elevation. The dry adiabatic lapse rate of 9.8°C/km combined with a dew point lapse rate of about 1.8°C/km gives a convergence rate of approximately 8°C per 1000 m, meaning the temperature and dew point meet at 125 m per degree Celsius of spread.
What is the cloud base formula in imperial units?
In imperial units, cloud base altitude in feet = (temperature in °F - dew point in °F) / 4.4 × 1000 + elevation in feet. This uses the dry adiabatic lapse rate of 5.4°F per 1000 ft and a dew point lapse rate of approximately 1.0°F per 1000 ft, giving a convergence rate of 4.4°F per 1000 ft.
What is cloud base altitude?
Cloud base altitude is the lowest altitude above mean sea level at which clouds form. It is determined by the difference between air temperature and dew point at the surface. When air rises and cools adiabatically, it reaches saturation at the altitude where the temperature equals the dew point, forming the base of a cloud.
Is the Cloud Base Altitude Calculator free?
Yes, the Cloud Base Altitude Calculator is completely free to use with no registration or download required. You can use it unlimited times and share your calculations via URL.
Can I calculate cloud base altitude in both meters and feet?
Yes, the calculator shows results in both metric (meters, °C) and imperial (feet, °F) units simultaneously. Enter temperature and dew point in Celsius with elevation in meters, and get cloud base altitude in meters and feet plus cloud temperature in both Celsius and Fahrenheit.
What weather conditions affect cloud formation?
Cloud formation depends on air temperature, relative humidity (dew point), and atmospheric stability. When the temperature and dew point are close (small spread), clouds form at lower altitudes. A large spread means drier air requiring more lifting and cooling before condensation occurs.
How accurate is the cloud base altitude estimate?
The cloud base altitude formula provides a good estimate for convective clouds formed by rising air parcels. Accuracy depends on how well the actual atmospheric lapse rate matches the standard adiabatic lapse rate. Temperature inversions, humidity layers, and atmospheric stability can cause deviations from the calculated value.
What is the temperature of clouds at their base?
The cloud base temperature is calculated by applying the dry adiabatic lapse rate of 9.8°C per km (5.4°F per 1000 ft) from the surface to the cloud base altitude. For example, if surface temperature is 25°C and cloud base is at 2000 m, the cloud temperature would be approximately 25 - 9.8 × 2 = 5.4°C.