Cabin Pressure Differential Calculator

Work out cabin pressure differential instantly with clear inputs, formula shown and shareable results.

About Cabin Pressure Differential Calculator

Cabin differential is the cabin pressure minus the outside pressure, both taken from the standard atmosphere at their respective altitudes. Airframes are certified to a maximum differential, and that limit — not engine or system capacity — is what sets the cabin altitude achievable at a given cruise level.

Formula

Cabin differential

dP = P(cabin altitude) - P(cruise altitude), P(h) = 14.696 x (1 - 6.87535e-6 h)^5.2559 psi

Worked example

With the default values below, Cabin Pressure Differential Calculator returns Cabin differential pressure of 8.49. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cruise altitude: 39,000 ft
Cabin altitude: 7,000 ft
Maximum certified differential: 8.6 psi

Results

Cabin differential pressure: 8.49 psi
Cabin pressure: 11.34 psi
Ambient pressure: 2.85 psi
Margin to the certified limit: 0.11 psi

Step by step

1Values used
2Cabin differential
3Cabin differential pressure= 8.49 psi
4Cabin pressure= 11.34 psi
5Ambient pressure= 2.85 psi
6Margin to the certified limit= 0.11 psi

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Aviation results are planning estimates only. Always verify take-off, landing, fuel, weight and balance figures against the certified Aircraft Flight Manual, current performance charts and applicable aviation regulations before flight.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Aviation results are planning estimates only. Always verify take-off, landing, fuel, weight and balance figures against the certified Aircraft Flight Manual, current performance charts and applicable aviation regulations before flight.

Frequently Asked Questions

Why not keep the cabin at sea level?

The structure would need to withstand around 14 psi differential at high cruise levels, which means a much heavier fuselage. Cabin altitudes of 6,000-8,000 ft are the weight compromise.

What happens if the limit is exceeded?

Relief valves open to protect the structure, so cabin altitude rises. Repeated over-pressure cycles are a structural fatigue concern and must be recorded.