Aviation Training Experts

Aviation Training Experts™

Cloud Base Calculator

Estimate cloud base using temperature and dew point. This free aviation calculator helps pilots estimate cloud base AGL and optional cloud base MSL for weather awareness and flight planning.

Calculate Cloud Base

Enter temperature and dew point in Celsius to estimate cloud base above ground level. You can also enter field elevation to estimate cloud base above mean sea level.

Cloud Base from Temperature and Dew Point

How It Works

Cloud Base AGL:
(Temperature - Dew Point) × 400
Cloud Base MSL:
Cloud Base AGL + Field Elevation

This is a common aviation rule of thumb used to estimate the base of convective clouds from the temperature-dew point spread.

What Is Cloud Base?

Cloud base is the approximate height of the bottom of a cloud layer. Pilots often estimate cloud base using the spread between temperature and dew point.

When temperature and dew point are close together, the air is more nearly saturated, which means clouds can form at lower altitudes. A larger spread usually means a higher estimated cloud base.

Why Pilots Use a Cloud Base Calculator

Cloud Base FAQ

Is this an exact ceiling?

No. This is a rule-of-thumb estimate, not an official ceiling determination. Actual cloud layers can vary based on atmospheric conditions.

Why use Celsius?

This common aviation rule of thumb is usually expressed in degrees Celsius and feet AGL.

What if dew point is higher than temperature?

That usually indicates unrealistic input data or saturated conditions. In normal weather observations, dew point should not be higher than air temperature.

What is the difference between AGL and MSL?

AGL means above ground level. MSL means above mean sea level. Adding field elevation to cloud base AGL gives an estimated cloud base MSL.