Free pressure altitude calculator
Enter your altimeter setting — in inHg or hPa — and your field elevation to get the pressure altitude in feet, the altitude the standard atmosphere reads for the current pressure and the first input to density altitude, updated live, as you type.
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Planning estimate using the FAA/NWS field approximation. Always set and read your aircraft's altimeter and cross-check official performance data.
Results are estimates. Consult a professional.
What is pressure altitude?
Pressure altitude is the altitude in the International Standard Atmosphere (ISA) that matches the air pressure where you are. Put simply, it is the height your altimeter shows when its setting window is rolled to the standard datum of 29.92 inHg (1013.25 hPa). On a day when the local pressure differs from standard — which is almost every day — that height is not the same as the airport's elevation sign.
Pilots reach for pressure altitude constantly. It is the common reference that puts every aircraft on the same altimeter setting above the transition altitude, so traffic flying "flight levels" stays vertically separated. It is also the starting point for density altitude, true airspeed, and the takeoff and climb numbers in an aircraft's performance charts. This calculator turns two readings you already have — the altimeter setting and the field elevation — into pressure altitude in feet.
How the pressure altitude calculator works
The calculator uses the field approximation taught to pilots: compare the local altimeter setting with the standard 29.92 inHg, and add the difference — scaled by 1,000 feet per inch of mercury — to the field elevation. A handy version of the same rule is that every 0.01 inHg the setting sits below 29.92 raises pressure altitude by about 10 feet.
Why 29.92 inHg (1013.25 hPa) is the standard datum
Pressure altitude is measured against one agreed reference: the International Standard Atmosphere, which fixes sea-level pressure at 29.92 inHg, equal to 1013.25 hectopascals (also written 1013.25 millibars). Set an altimeter to that value and it reads pressure altitude directly — the height the standard atmosphere assigns to whatever pressure the instrument senses.
Real weather rarely sits exactly at the datum. A deep low can drop the local setting well below 29.92, and a strong high can push it above. Because pressure falls with height, a lower surface pressure looks to the altimeter like a greater height — so a below-standard setting makes pressure altitude climb above the field, and an above-standard setting pulls it below. The 1 inHg ≈ 1,000 ft scaling in the formula is simply how fast the standard atmosphere changes pressure near the surface.
The two inputs: altimeter setting and field elevation
Only two numbers drive pressure altitude, and each does a distinct job.
Altimeter setting (QNH)
The local sea-level-equivalent pressure broadcast by ATIS, a tower, or a weather station — 29.45 inHg or 1005 hPa, for example. It is the only weather-driven input, and it is what separates pressure altitude from plain field elevation. Toggle the unit and the calculator handles inHg or hPa.
Field / station elevation
The height of the airport or station above mean sea level, in feet. It is fixed for any given location and sets the base that the pressure correction is added to. Use the published field elevation, not your indicated altitude in the air.
A worked example using the pressure altitude calculator
A pilot is preparing to depart a mountain airport at 4,500 ft elevation. ATIS gives the altimeter setting as 29.45 inHg — below standard, as a weather system moves through. Before working out density altitude and takeoff distance, they need the pressure altitude.
Step 1 — Find the pressure correction
29.92 − 29.45 = 0.47 inHg below standard. Multiply by 1,000: 0.47 × 1,000 = +470 ft. The low pressure makes the air "read" 470 feet higher than the field.
Step 2 — Add the field elevation
4,500 + 470 = 4,970 ft pressure altitude. That, not the 4,500 ft on the elevation sign, is the height the standard atmosphere reads for today's pressure — and the number to carry into the density altitude and performance calculations.
Pressure altitude by altimeter setting and field elevation
This chart shows pressure altitude (feet) for common altimeter settings at three field elevations. Read down to your altimeter setting, across to your field elevation. Each row is just the field elevation shifted by the pressure correction — about 1,000 ft for every full inch of mercury away from 29.92.
| Altimeter setting | Sea level | 2,500 ft | 5,000 ft |
|---|---|---|---|
| 29.42 inHg (996 hPa) | +500 ft | 3,000 ft | 5,500 ft |
| 29.92 inHg (1013 hPa) | 0 ft | 2,500 ft | 5,000 ft |
| 30.42 inHg (1030 hPa) | −500 ft | 2,000 ft | 4,500 ft |
Pressure altitude in feet from the FAA/NWS field approximation. At the standard 29.92 inHg setting pressure altitude equals field elevation; a setting 0.50 inHg either side moves it 500 ft. The hPa equivalents are rounded.
Pressure altitude and density altitude
Pressure altitude is the first half of the performance story; density altitude is the second. Pressure altitude corrects field elevation for non-standard pressure. Density altitude takes that pressure altitude and corrects it again for non-standard temperature — and, in reality, humidity. It is density altitude, not pressure altitude, that your wings and engine actually feel.
On a hot day the temperature correction is large, so density altitude sits well above pressure altitude. That is why pressure altitude is computed first: feed this result, plus the outside air temperature, into the density altitude calculator to get the altitude your aircraft truly performs at. For the related cloud question, the cloud base calculator estimates where fair-weather cumulus forms above the field.
How accurate is this pressure altitude calculator?
For the altimeter-setting input this calculator is effectively exact within the lower atmosphere. The 1,000 ft per inch of mercury scaling is the standard field rule, and from a normal altimeter setting at a normal field elevation it returns the same pressure altitude you would get by rolling the altimeter to 29.92 and reading the dial. The hPa path is precise too, using the exact 1 inHg = 33.8639 hPa conversion rather than the rounded "30 ft per hPa" shortcut.
Two limits are worth knowing. First, the 1 inHg ≈ 1,000 ft rate is the near-surface average; the standard atmosphere's pressure-to-height relationship curves gently with height, so very far from sea level the linear rule drifts by a small amount. Second, pressure altitude is a pressure reference only — it says nothing about how the air will perform. For takeoff, climb, and engine output you must carry it forward into density altitude, and for any flight you should rely on your altimeter, your aircraft's published performance data, and an official weather briefing rather than a calculator.
Pressure altitude definitions
Frequently asked questions about the free pressure altitude calculator
About this Pressure altitude calculator
This calculator runs entirely in your browser. Nothing you enter is sent anywhere — your altimeter setting and field elevation stay on your device, and the pressure altitude updates instantly as you adjust them.
It applies the FAA/NWS field approximation and pairs with the density altitude calculator and cloud base calculator. Browse the full set of weather calculators or the whole calculator library.