E6BPilot Computer
Free calculator

Cloud base calculator

An estimate of the cloud base from temperature and dew point, above the field and above sea level, with the working shown. Results update as you type.

Example values — change any of them
°C

Surface temperature, from the METAR.

°C

Surface dew point, from the METAR.

ft

Field elevation, for the base above sea level.

Units
Cloud Base (AGL)
3,200 ft
Cloud Base (MSL)
4,200 ft

Cloud base about 3,200 ft above the field, 4,200 ft above sea level.

AGL = (OAT − DP) × 400MSL = AGL + elevRule of thumb: base rises ≈400 ft per °C of temperature–dew point spread. DP is the dew point. Computed in ft · °C.

Worked example — with your numbers

  1. AGL = (24 − 16) × 400 = 3,200 ft
  2. MSL = 3,200 + 1,000 = 4,200 ft

Why the spread gives the base

Rising air cools at about 3 °C per 1,000 ft until it saturates, while its dew point falls by only about 0.5 °C per 1,000 ft. The two close at roughly 2.5 °C per 1,000 ft, so each degree of temperature–dew point spread is about 400 ft of height to the base.

When the estimate applies

It estimates the base of cumulus that forms as the ground heats the air above it. It does not forecast fog, low stratus or cloud that arrives with a front, and it is no substitute for a reported ceiling.

Density altitudePressure altitudeCrosswindUnit converterWeight and balance

Solve it on your iPhone. The same cloud base math, a keypad built for the cockpit, and METAR paste that fills in temperature and dew point. The free calculators stay free.

App Store · coming soon
Safety

For training and supplemental situational awareness only. Not for use as the sole basis for flight planning, performance, or operational decisions. It is not an approved flight planning tool, electronic flight bag (EFB), or primary source of aeronautical information. Always use current aircraft documents, an official briefing, and pilot judgment.