Cloud Base Altitude Calculator
Estimating the base altitude of convective clouds is a practical skill in meteorology and aviation weather briefing. The standard method uses the dewpoint depression (the difference between surface temperature and dewpoint) and applies the known dry adiabatic and dewpoint lapse rates to find the altitude at which a rising air parcel reaches saturation. At that altitude, called the lifted condensation level (LCL), cloud formation begins. This calculator gives the result in feet above ground level (AGL), matching aviation reporting conventions.
Cloud base formula
Cloud Base (ft AGL) = (T - Td) / 4.4 * 1000
T is surface temperature in degrees Fahrenheit, Td is dewpoint in degrees Fahrenheit. The factor 4.4 F per 1,000 feet is the difference between the dry adiabatic lapse rate (5.4 F/1,000 ft) and the dewpoint lapse rate (1.0 F/1,000 ft). Cloud base in meters = cloud base in feet * 0.3048.
Interpreting cloud base estimates
- High bases (above 10,000 ft): typical of dry continental air masses; common in the western US in summer.
- Low bases (below 3,000 ft): associated with moist air, potential reduced visibility, instrument flight conditions.
- Aviation minimums: VFR typically requires ceilings above 3,000 ft AGL with 5 miles visibility; IFR applies when ceilings are below.
- Storm bases: severe thunderstorms can have bases of 5,000-8,000 ft over the High Plains, aiding in tornado assessment.
Cloud base calculator: frequently asked questions
How is cloud base altitude estimated from temperature and dewpoint?
The standard estimate is: cloud base (feet AGL) = (T - Td) / 4.4 * 1000, where T is surface temperature in Fahrenheit and Td is dewpoint in Fahrenheit. The denominator 4.4 comes from the difference in dry adiabatic lapse rate (5.4 F/1000 ft) and the dewpoint lapse rate (1 F/1000 ft), which is 4.4 F per 1000 feet.
Is this the same as the lifted condensation level (LCL)?
Yes. The formula estimates the lifted condensation level, which is the altitude at which a parcel of air lifted dry-adiabatically will become saturated and clouds will begin to form. Cumuliform clouds have their base near the LCL.
How accurate is this estimate?
The rule is accurate for fair-weather cumulus clouds on days with good convective mixing. It is less reliable for stratus, fog, or inversions. The actual cloud base also depends on moisture distribution with height and atmospheric instability. Aviation uses this as a quick cross-check of METAR or forecast data.
What is the metric version of this formula?
In metric units, cloud base (meters) = (T - Td) / 0.8 * 1000, where temperatures are in Celsius. The divisor 0.8 is the Celsius equivalent of 4.4 F per 1000 ft (approximately 2.4 C per 300 m), giving meters above ground level.
Does this formula apply to all cloud types?
No. This method applies specifically to convective (cumuliform) cloud bases. Stratiform clouds, fog, and high-altitude ice clouds form by different mechanisms. The National Weather Service and aviation meteorology use this formula as a quick check for afternoon thunderstorm and cumulus cloud forecasting.
Official sources
- NOAA/NWS: JetStream: Clouds.
- FAA Aeronautical Information Manual: AIM Chapter 7: Safety of Flight.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.