Pressure Altitude Calculator | Standard Atmosphere

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Quick check

Choose one mode first: pressure to altitude, altitude to pressure, or sea-level pressure.

Keep units consistent from start to end.

Use the model that matches your case, then compare with local weather data.

For flight or safety operations, always use certified sources.

Inputs

Calculation type

Atmospheric pressure → altitude Altitude → atmospheric pressure Sea level pressure

Observed atmospheric pressure (P)

Observation point altitude (z)

Options (model, sea level pressure, and temperature)

Model

Standard atmosphere (troposphere approximation) Isothermal (constant temperature)

Sea level pressure (P0)

Use the sea-level pressure shown on weather maps (standard value: 1013.25 hPa).

Results are automatically updated on input changes (can be restored with share URL).

Results

Calculation type: — / Model: —

—

Sea level pressure (P0)	—
Air temperature (isothermal model)	—

Graph (atmospheric pressure-altitude)

Hover over the graph, or tap it on a phone, to read the value at that point.

Calculation assumptions and formulas (overview)

This tool uses "standard atmosphere (tropospheric approximation)" as its main axis, and converts using "isothermal approximation (constant temperature)" as necessary.

Standard atmosphere (tropospheric approximation/ISA)

Altitude → atmospheric pressure: P = P0 * (1 - (L*z)/T0)^a

Atmospheric pressure → altitude: z = (T0/L) * (1 - (P/P0)^n)

Sea level correction (estimate): P0 = P_station / (1 - (L*z)/T0)^a

Approximate range: -500 to 11000 m (warning outside range).

Isothermal approximation (constant temperature)

Altitude → atmospheric pressure: P = P0 * exp(-g0*z/(Rspec*T))

Atmospheric pressure → altitude: z = (Rspec*T/g0) * ln(P0/P)

Sea level correction (estimate): P0 = P_station * exp(g0*z/(Rspec*T))

This is only an approximation, as the actual atmosphere is not isothermal.

How to use this pressure altitude calculator

Pick the mode that matches the reading you already have, then keep the model and unit system fixed until the result looks reasonable.

Use it in 3 steps

Choose pressure → altitude, altitude → pressure, or sea level pressure.
Enter the observed value with the correct unit and keep metric or US units consistent from input to output.
Select the standard-atmosphere model for a baseline, then compare with the isothermal model only if temperature sensitivity matters.

What this page helps with

This tool is useful for weather, hiking, classroom, and engineering estimates where you want a quick pressure-altitude conversion or a sea-level-pressure correction from local readings.

Common mistakes to avoid

Using the wrong mode and then trying to compensate by changing other inputs.
Mixing hPa, kPa, Pa, and inHg across the same scenario.
Comparing a quick estimate here with operational aviation data as if they were the same source.
Changing the model before you verify the baseline result with standard atmosphere.

Worked example

If you have a station pressure and site altitude, start with the sea-level-pressure mode to estimate the corrected pressure. If you only have one local pressure reading and want a rough height, start with pressure to altitude and compare the result with known terrain or weather data.

Frequently asked questions

What is sea level pressure (P0)?

Sea-level pressure is the station pressure adjusted to mean sea level for weather maps and altimeter settings. This calculator uses 1013.25 hPa as the standard pressure reference.

Why does the atmospheric pressure change even in the same place?

Air pressure can change at the same altitude because weather systems, temperature, and humidity change the local air mass.

How accurate is a mountaineering altimeter (barometer)?

A barometric altimeter can drift as weather changes. Updating sea-level pressure (P0) to the current local value can improve the estimate, but it is still not a certified aviation source.

When should you use an isothermal model?

Use it when you want a rough temperature-sensitive estimate. The real atmosphere changes temperature with altitude, so this model is not suitable for precision work.

Which mode should I choose first?

Choose pressure to altitude when you have a local pressure reading, altitude to pressure when you already know the height, and sea level pressure when you want to correct a station reading to sea level.

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