What formula does this tool use?

The tool uses the standard aviation approximation: Cloud Base (ft) = (T - Td) × 400.6, where T is surface temperature and Td is dew point in °F. In metric terms, Cloud Base (m) ≈ (T - Td in °C) × 122. This approximation is accurate for well-mixed, convectively unstable air masses and is taught in FAA and EASA ground school curricula.

What is the lifting condensation level (LCL)?

The LCL is the altitude at which a parcel of air, lifted dry-adiabatically from the surface, cools to its dew point and becomes saturated. This is the theoretical base of cumulus clouds. The cloud base calculator estimates the LCL from surface observations.

Can the dew point be higher than the surface temperature?

No. The dew point is always equal to or lower than the air temperature. If you enter a dew point higher than the temperature, the tool will display an error. When they are equal (spread = 0), the air is saturated and clouds form at or near the surface — often as fog or stratus.

How accurate is this estimate?

The formula gives a good first approximation for convective (cumulus-type) clouds. It assumes a standard dry adiabatic lapse rate and well-mixed boundary layer. Actual cloud bases can differ due to wind shear, terrain, inversions, and complex atmospheric layering. Always cross-check with official aviation weather products such as TAFs and METARs.

What spread indicates cloud formation near the surface?

A spread of 2 °F (about 1 °C) or less suggests clouds or fog at very low altitudes. A spread of 0 means the air is already saturated at the surface. Pilots typically look for a spread of 5 °F or more to ensure safe visual flight conditions.

Does this apply to all cloud types?

This calculator estimates the base of convective clouds (cumulus and cumulonimbus). It does not apply to stratiform clouds (stratus, altostratus, cirrostratus) that form through large-scale lifting, radiational cooling, or frontal dynamics rather than surface-driven convection.

Cloud Base Calculator

Name: Cloud Base Calculator
Availability: InStock
Author: Nham Vu

Enter surface temperature and dew point to instantly estimate the altitude of the cloud base in feet and meters.

Surface Conditions

Temperature Unit

Surface Temperature (°F)

Dew Point Temperature (°F)

Must be equal to or lower than surface temperature.

Spread Reference

Spread (T - Td) Approx. Cloud Base

2 °F (1 °C)~800 ft / 240 m

5 °F (2.8 °C)~2,000 ft / 610 m

10 °F (5.6 °C)~4,000 ft / 1,220 m

20 °F (11 °C)~8,000 ft / 2,440 m

30 °F (16.7 °C)~12,000 ft / 3,660 m

Enter surface temperature and dew point,
then click Calculate Cloud Base.

Estimated Cloud Base

feet AGL

meters AGL

Surface Temp

Dew Point

Spread

Aviation Ceiling Reference

Near Surface / Fog

Below 500 ft (152 m)

Low Ceiling

500–1,500 ft (152–457 m)

Marginal VFR

1,500–3,000 ft (457–914 m)

VFR Conditions

3,000–6,000 ft (914–1,829 m)

Good Ceiling

Above 6,000 ft (1,829 m)

Formula: Cloud Base (ft) = (T − Td) × 400.6. AGL = Above Ground Level.

Summary

Enter surface temperature and dew point to instantly estimate the altitude of the cloud base in feet and meters.

How it works

Enter the surface air temperature in Fahrenheit or Celsius.
Enter the surface dew point temperature in the same unit.
The tool computes the temperature-dew point spread (T minus Td).
Cloud base altitude is estimated at roughly 400 ft per °F of spread (or 122 m per °C).
Results are displayed in both feet and meters with an aviation context rating.

Use cases

Estimate cumulus cloud base height before a flight.
Assess soaring conditions for glider and sailplane pilots.
Anticipate thunderstorm base altitude during severe weather analysis.
Plan outdoor activities that depend on low-level cloud cover.
Teach meteorology students about the lifting condensation level (LCL).
Cross-check METAR cloud data with surface observations.
Evaluate paragliding and hang-gliding thermal conditions.
Understand how humidity affects cloud formation height.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu