Air Pressure at Altitude Calculator and Formula

An air pressure at altitude calculator estimates atmospheric pressure from elevation using the standard-atmosphere model. Enter altitude in metres or feet and it returns pressure in pascals, kilopascals, or another chosen pressure unit; the estimate assumes standard conditions, not the day’s measured weather.

Formula

This calculator uses the standard-atmosphere relationship for the lower atmosphere:

p = p₀ × (1 − h / 44,330)^5.255

• p is estimated absolute air pressure in kilopascals (kPa).
• p₀ is standard sea-level pressure, 101.325 kPa.
• h is altitude above the standard sea-level reference, in metres.
• 44,330 m and the exponent 5.255 are constants in this approximate standard-atmosphere formula.

The second output is the result divided by standard sea-level pressure and multiplied by 100. It indicates the estimated pressure as a percentage of the sea-level standard. The model is intended for the troposphere, roughly the lowest 11 km of the standard atmosphere; this calculator’s input limit is 44,330 m because the expression ceases to represent a meaningful positive pressure at or above that value. For dependable atmospheric calculations at high altitude, use an appropriate layered-atmosphere model rather than extending this equation.

Worked Example

Using the default altitude of 1,000 m:

1. Substitute the altitude: p = 101.325 × (1 − 1,000 / 44,330)^5.255.
2. Evaluate the bracket: 1 − 1,000 / 44,330 ≈ 0.97744.
3. Raise it to the power 5.255 and multiply by 101.325: p ≈ 90.022 kPa.
4. Rounded to two decimal places, estimated pressure is 90.02 kPa.
5. Pressure relative to sea-level standard is 100 × 90.022 / 101.325 ≈ 88.85%.

The altitude input is in metres. To use a height given in feet, convert it first: 1 ft = 0.3048 m. For example, 5,000 ft is 1,524 m. Do not enter 5,000 directly into this calculator unless the height is 5,000 metres.

What altitude pressure means

Air pressure is the force per unit area exerted by the air above a location. At higher elevations, there is generally less air overhead, so pressure falls. Pressure is not the same as air density, though the two are related: density also depends on temperature and humidity, while pressure reflects the weight and state of the air column.

At sea level, the standard-atmosphere reference is 101.325 kPa, equivalent to 1,013.25 hectopascals (hPa), 1,013.25 millibars, or about 14.696 pounds per square inch (psi). These are equivalent units for the same reference pressure. Real sea-level pressure changes with weather, so 101.325 kPa is a model baseline, not a guarantee about a particular location or time.

Pressure decreases nonlinearly with altitude. A rise of 1,000 metres does not subtract the same fixed pressure as the next 1,000 metres. The air becomes thinner as height increases, and the relationship depends on the temperature structure assumed by the model.

When to use the estimate

This estimate is useful for understanding how elevation affects atmospheric pressure, checking an approximate value for a location, or comparing elevations under the same standard assumptions. It can also help interpret why pressure readings and pressure-based measurements differ between locations.

• Use altitude above sea level, rather than height above a nearby valley or building.
• Use the same altitude unit the calculator requests; convert feet to metres before entering the value.
• Read the result as absolute atmospheric pressure, not gauge pressure. Gauge pressure is measured relative to ambient air.
• For a current local pressure, consult a weather observation or barometer. The calculator does not account for current weather.

Pressure may be reported as station pressure or as sea-level pressure adjusted from a station reading. Those values answer different questions. A weather report’s sea-level-adjusted number is not the actual pressure at a high-elevation station, so compare like with like.

Standard atmosphere versus real conditions

The standard atmosphere is a convenient reference model: it specifies a standard pressure and temperature profile so that elevations can be compared consistently. It is not a live forecast. Actual pressure at a given altitude varies as weather systems move, and temperature departures from the standard profile also affect the pressure-height relationship.

For a more precise estimate, use a model that includes measured temperature and, where relevant, humidity and local pressure. A nearby calibrated barometer or meteorological station can provide observed conditions. Observations themselves have uncertainty and may be at a different elevation or location, so check what the reported pressure represents.

Pressure also changes over time at a fixed location. A passing weather system can change the reading without any change in elevation. This is why a calculator based only on altitude cannot reproduce a current barometer reading exactly.

Units and common mistakes

The calculator displays kPa, while pressure instruments and reports may use hPa, millibars, psi, or inches of mercury (inHg). Useful conversions include 1 kPa = 10 hPa = 10 millibars, and 1 psi ≈ 6.895 kPa. Make sure the units match before comparing numbers. For example, 90 kPa is 900 hPa, not 90 hPa.

• Mixing altitude units: feet entered as metres produce a substantially incorrect estimate.
• Confusing absolute and gauge pressure: atmospheric pressure is absolute pressure; gauge pressure is relative to surrounding air.
• Treating the answer as a live reading: the calculation does not include weather, local temperature, or measurement conditions.
• Over-interpreting rounded values: two decimal places are a display choice, not a claim that the real atmosphere is known to that precision.

Limits and choosing a method

For a quick, consistent estimate in the lower atmosphere, the calculator’s standard formula is suitable. If you need a real-time value, use an instrument or an authoritative local observation and note whether it reports station pressure or a sea-level adjustment. For engineering, scientific, or aviation work, use the specified atmospheric model and data source for that application; this simple calculator is not a substitute for required operational information.

Altitude itself can also be defined in different ways. Surveyed elevation, GPS altitude, and pressure-derived altitude may not match exactly. The calculator assumes a known altitude above sea level, so uncertainty in the altitude input carries through to the pressure estimate. At high elevations or near the model’s limits, do not rely on this simplified equation without checking a suitable reference model.

Frequently Asked Questions

How do I calculate air pressure at altitude?
For the standard lower-atmosphere estimate, use p = 101.325 × (1 − h / 44,330)^5.255, with altitude h in metres and pressure p in kPa. The calculator applies this formula automatically.

What is the air pressure at 1,000 metres?
The standard-atmosphere estimate is about 90.02 kPa, or 88.85% of standard sea-level pressure. Weather and temperature can make an observed value different.

Does air pressure decrease linearly with altitude?
No. It decreases nonlinearly. The amount of pressure change for each additional metre depends on altitude and the atmospheric conditions represented by the model.

Can I enter altitude in feet?
This calculator accepts metres. Convert feet to metres by multiplying by 0.3048; for example, 5,000 ft equals 1,524 m.

Why is my barometer reading different from the calculator?
The calculator uses standard-atmosphere assumptions, while a barometer measures local conditions. Weather, temperature, instrument calibration, and whether a report is adjusted to sea level can all explain a difference.

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in h | Altitude | m | 1000 | 0 | 44330
out p | Air pressure | kPa | 101.325 * (1 - h / 44330)^5.255 | 2
out ratio | Pressure as percent of sea-level standard | % | 100 * p / 101.325 | 2