Pressure Altitude Calculator
Find your pressure altitude from the field elevation and altimeter setting, with the exact formula and the quick rule side by side.
We read the pressure (A2982 or Q1003) and the temperature and fill them in. Type the field elevation yourself.
The airport's height above sea level, from the chart or airport directory.
In a METAR, A2982 means 29.82 inHg and Q1003 means 1003 hPa.
You see both either way. This picks which one is the big answer.
For ISA deviation and density altitude. Leave empty to skip.
18,000 ft in the US. Many countries use 3,000 to 6,000 ft or more. Check your AIP.
How your pressure altitude is worked out
Compare the pressure with standard, turn the gap into feet, then add it to where you are.
- 1
Gap from standard
29.92 − 29.82
= 0.10 inHg - 2
Turn it into feet
ISA: +94 ft
Rule: +100 ft - 3
Add the field
5,000 + 94
= 5,094 ft - 4
Standard temperature
15 − 1.981 × 5.09
= 4.9 °C · FL051
Read more: the formula, the quick rules, a METAR example and transition levels
Pressure altitude is the height your altimeter shows when it is set to standard pressure: 29.92 inHg, 1013.25 hPa or 760 mmHg. It is your height in the International Standard Atmosphere (ISA), worked out from pressure alone. Pilots use it for flight levels and for reading performance charts, and it is the starting point for density altitude.
The formula
pressure altitude = elevation + 145,442 × (1 − (altimeter setting in hPa ÷ 1013.25)^0.190263) ft
quick rule (inHg) = elevation + (29.92 − setting) × 1,000 ft
quick rule (hPa) = elevation + (1013.25 − setting) × 30 ft (or × 27 ft)
from station pressure (QFE) = 145,442 × (1 − (QFE ÷ 1013.25)^0.190263) ft
ISA temperature = 15 − 1.98 × pressure altitude in thousands of feet (°C)
flight level = pressure altitude ÷ 100
The exact formula is the one an altimeter is built on: it reads the pressure altitude of the air around it minus the pressure altitude of the setting in its window. In flight, put the altimeter reading in place of the elevation. 1 inHg = 33.8639 hPa and 1 mmHg = 1.33322 hPa. The quick rules are close near sea level and drift a little at high settings or high airfields, which is why the calculator shows the difference.
Worked example
Say the METAR for your 5,000 ft airfield reads ZZZZ 111150Z 27008KT 9999 FEW050 25/08 A2982. A2982 is an altimeter setting of 29.82 inHg, and 25/08 means 25 °C with a dew point of 8 °C.
- Gap from standard: 29.92 − 29.82 = 0.10 inHg. In hPa, 29.82 × 33.8639 = 1009.82 hPa, which is 1013.25 − 1009.82 = 3.43 hPa below standard.
- Exact: 145,442 × (1 − (1009.82 ÷ 1013.25)^0.190263) = 94 ft, so the pressure altitude is 5,000 + 94 = 5,094 ft.
- Quick rule: 5,000 + 0.10 × 1,000 = 5,100 ft, 6 ft more than exact. With 30 ft per hPa it is 5,000 + 3.43 × 30 = 5,103 ft, and with 27 ft per hPa 5,093 ft.
- ISA temperature at 5,094 ft: 15 − 1.98 × 5.094 = 4.9 °C. At 25 °C the air is 20.1 °C warmer than standard (ISA +20).
- Density altitude: about 7,380 ft (7,376 ft). The 120 ft per °C rule gives 5,094 + 120 × 20.1 = 7,506 ft.
- Station pressure (QFE): 840.1 hPa, or 24.81 inHg.
- Flight level: 5,094 ÷ 100 = FL051. With an 18,000 ft transition altitude, 18,000 + 94 = 18,094 ft is FL180.9, so the lowest flight level above it is FL185.
Quick rules compared
| Field and QNH | Exact | 1,000 ft per inHg | 30 ft per hPa | 27 ft per hPa |
|---|---|---|---|---|
| 5,000 ft · 29.82 inHg | 5,094 ft | 5,100 ft | 5,103 ft | 5,093 ft |
| 1,000 ft · 1003 hPa | 1,281 ft | 1,301 ft | 1,308 ft | 1,277 ft |
Transition altitude and transition level
Below the transition altitude you fly altitudes with the local QNH set. At and above the transition level you fly flight levels with standard pressure set. The transition level is the lowest flight level above the transition altitude (plus any transition layer a country asks for), so it goes up when the QNH is low. This calculator steps flight levels in fives (FL35, FL40, FL45). In the United States the transition altitude is 18,000 ft, and 14 CFR 91.121 sets the lowest usable flight level: FL180 at 29.92 inHg or higher, FL185 from 29.91 to 29.42, FL190 from 29.41 to 28.92, and 5 more for every further 0.50 inHg down to FL210 at 26.92. Other countries publish their own values in their AIP.
Station pressure (QFE)
Station pressure is the actual pressure at the airfield. With QFE set, an altimeter reads zero on the ground, so the pressure altitude of the field is simply the pressure altitude of the QFE. In Advanced you can enter QFE (common in some military, gliding and CIS operations, often in mmHg) and the calculator works the QNH out from the elevation.
The US National Weather Service density altitude tool turns the altimeter setting into station pressure with a slightly different shortcut, so its pressure altitude can differ from this one by up to about 10 ft at a high airfield. For take-off planning use the density altitude calculator, and for QNH, QFE and unit changes the altimeter setting calculator.
For planning and education. Use official reports, ATC instructions and your aircraft's approved performance charts.
Common questions
How do you calculate pressure altitude?
Take the field elevation and add the height for the gap between the altimeter setting and standard pressure (29.92 inHg or 1013.25 hPa). A 5,000 ft field with 29.82 inHg is 0.10 inHg below standard, so the quick rule gives 5,000 + 0.10 × 1,000 = 5,100 ft. The exact standard-atmosphere formula gives 5,094 ft.
Is it 1,000 ft per inch or 30 ft per hPa?
Both are rules of thumb. 1,000 ft per inHg is the same as about 29.5 ft per hPa. Near sea level the standard atmosphere is closer to 27 ft per hPa. At a 1,000 ft field with QNH 1003 hPa, 30 ft per hPa gives 1,308 ft, 27 ft per hPa gives 1,277 ft and the exact formula gives 1,281 ft.
What is the difference between pressure altitude and density altitude?
Pressure altitude is what the altimeter reads with 29.92 inHg or 1013.25 hPa set. It only corrects for pressure. Density altitude also corrects for temperature, so it shows how the aircraft will perform. At a 5,000 ft field with 29.82 inHg and 25 °C, the pressure altitude is 5,094 ft but the density altitude is about 7,380 ft.
Why is pressure altitude used for flight levels?
Above the transition altitude every aircraft sets the same standard pressure, so their altimeters all measure from the same level and stay correctly separated. A flight level is simply the pressure altitude in hundreds of feet: 5,094 ft is FL051. Below the transition altitude pilots use the local QNH so the altimeter shows height above sea level.
What is the transition level?
It is the lowest flight level above the transition altitude, so it moves with the QNH. In the United States the transition altitude is 18,000 ft. With 29.82 inHg, 18,000 ft is pressure altitude 18,094 ft, so FL180 is below it and FL185 is the lowest usable level, which matches the US rule table for 29.91 to 29.42 inHg.
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Made by Zulu Calculator, part of AlphaZulu LLC. Formulas are shown in full and rule figures are checked against official sources; see how we build calculators.