Cold Temperature Correction Calculator
Add the right amount to every approach altitude when the airfield is cold, from the FAF down to the MDA or DA.
Altitudes above sea level, as printed on the approach chart. Use the MDA or DA itself, not the height (HAT/HAA).
ICAO Doc 8168 formula: uses the airport elevation and the height above the altimeter setting source.
Only if the QNH or altimeter setting comes from somewhere else (a remote source). The correction applies to the height above the source.
How your cold temperature correction is worked out
Cold air is dense, so the pressure levels squash together and you are lower than the altimeter shows.
- 1
ISA at the field
15 − 1.98 × 1.0
= 13.0 °C ISA
ISA −38.0 °C - 2
Height above source
3,000 − 1,000 ft
= 2,000 ft above - 3
The ICAO formula
2,000 × 38.02
÷ 247.01
= +308 ft - 4
Round up and fly
3,000 + 308 ft
up to next 100 ft
= 3,400 ft
Read more: the formula, a worked example, the ICAO table and US cold temperature airports
An altimeter measures pressure and turns it into height using the standard atmosphere (ISA): 15 °C at sea level, cooling 1.98 °C for every 1,000 ft. Cold air is denser than that, so the pressure levels sit closer together. Fly a published altitude in cold air and you are lower than the altimeter shows, which eats into the obstacle clearance the procedure was built with. The fix is to add a correction to the published altitudes. For a single altitude and the wrong-setting error, the altimeter setting calculator is quicker; this page corrects a whole approach.
The formula
t0 = airport temperature + 0.00198 × airport elevation (ft)
correction = H × (15 − t0) ÷ (273 + t0 − 0.5 × 0.00198 × (H + Hss))
H = published altitude − altimeter setting source elevation
Hss = altimeter setting source elevation (normally the airport)
altitude to fly = published altitude + correction, rounded up
4% rule: correction ≈ H × 4% × (degrees below ISA ÷ 10)
ISA at the airport = 15 − 0.00198 × elevation (°C)
This is the approximate formula in ICAO Doc 8168 (PANS-OPS). In metres use 0.0065 °C per m in place of 0.00198, and H in metres. The "full integration" method works through the standard atmosphere layer by layer with the same temperature difference from ISA all the way up. It is a cross-check and lands within a few feet of the formula.
Worked example
An airport 1,000 ft above sea level reports −25 °C. The approach has an IF at 4,000 ft, a FAF at 3,000 ft, a step-down at 2,000 ft, an MDA of 1,500 ft and a missed approach altitude of 4,000 ft.
- ISA at the airport is 15 − 0.00198 × 1,000 = 13.02 °C, so −25 °C is 38.02 °C below ISA.
- t0 = −25 + 0.00198 × 1,000 = −23.02 °C, so 15 − t0 = 38.02.
- FAF: H = 3,000 − 1,000 = 2,000 ft. Correction = 2,000 × 38.02 ÷ (273 − 23.02 − 0.5 × 0.00198 × 3,000) = 76,040 ÷ 247.01 = 308 ft. 3,000 + 308 = 3,308 ft, rounded up to 3,400 ft.
- Step-down: H = 1,000 ft. 38,020 ÷ 248.00 = 153 ft, so 2,153 ft, rounded up to 2,200 ft.
- MDA: H = 500 ft. 19,010 ÷ 248.50 = 76.5 ft, so 1,576.5 ft, rounded up to the next 10 ft: 1,580 ft.
- IF and missed approach: H = 3,000 ft. 114,060 ÷ 246.02 = 464 ft, so 4,464 ft, rounded up to 4,500 ft.
- 4% rule check for the FAF: 2,000 × 4% × 3.802 = 304 ft, 4 ft less than the formula.
- Flown uncorrected, the 3,000 ft FAF would put you at about 2,733 ft, 267 ft lower than the chart expects.
ICAO cold temperature error table
Feet to add, by height above the airport (rows) and reported airport temperature (columns). This is the table layout used in ICAO Doc 8168 and the FAA AIM (Table 7-3-1). It assumes a sea-level airport, so it is a little more generous than the formula at higher airports. Between the printed rows and columns the calculator interpolates in a straight line, and above 5,000 ft or below −50 °C it uses the formula instead.
| Height | +10 °C | 0 °C | −10 °C | −20 °C | −30 °C | −40 °C | −50 °C |
|---|---|---|---|---|---|---|---|
| 200 ft | 10 | 20 | 20 | 30 | 40 | 50 | 60 |
| 300 ft | 10 | 20 | 30 | 50 | 60 | 80 | 90 |
| 400 ft | 10 | 30 | 40 | 60 | 80 | 100 | 120 |
| 500 ft | 10 | 30 | 50 | 70 | 100 | 120 | 150 |
| 600 ft | 20 | 40 | 60 | 90 | 120 | 150 | 180 |
| 700 ft | 20 | 40 | 70 | 100 | 140 | 170 | 210 |
| 800 ft | 20 | 50 | 80 | 120 | 150 | 190 | 240 |
| 900 ft | 20 | 50 | 90 | 130 | 170 | 220 | 270 |
| 1,000 ft | 20 | 60 | 100 | 140 | 190 | 240 | 300 |
| 1,500 ft | 30 | 90 | 150 | 210 | 280 | 360 | 450 |
| 2,000 ft | 40 | 120 | 200 | 280 | 380 | 480 | 590 |
| 3,000 ft | 60 | 170 | 290 | 420 | 570 | 720 | 890 |
| 4,000 ft | 80 | 230 | 390 | 570 | 760 | 970 | 1,190 |
| 5,000 ft | 90 | 280 | 490 | 710 | 950 | 1,210 | 1,500 |
US cold temperature airports (FAA)
- The FAA publishes a list of Cold Temperature Airports. Their approach charts carry a snowflake symbol and a temperature, for example −20 °C.
- When the reported airport temperature is at or below that temperature, correct the altitudes in the segments the list marks: intermediate, final, missed approach, or all of them.
- Use the reported airport temperature and the height above the airport with the ICAO table (AIM 7-3).
- Tell ATC when you fly a corrected altitude in the intermediate or missed approach segment. You don't need to for the final segment.
- Don't correct altitudes ATC assigns on radar vectors, and never change the altimeter setting to make a correction.
Other countries
ICAO leaves the details to each state. Some, such as Canada (Transport Canada AIM, RAC 9.17), publish their own table and set the temperature at which corrections start. Australia (CASA and Airservices AIP) and Europe have their own notes too. Check your AIP, the chart notes and your operator's procedures for which altitudes to correct and how to round them.
Notes
- The correction depends on the height above the altimeter setting source, not the height above sea level. That is why a high MSA far above the field needs a much bigger correction than the MDA.
- Baro-VNAV approaches have their own lowest temperature on the chart. Below it, the vertical path can't be used unless the aircraft corrects for temperature.
- No correction is shown when the airport is at or above ISA.
Planning and training aid only. Always use your approved flight manual, operator procedures and official charts. The ICAO table and the AIM 7-3 Cold Temperature Airport rules were checked on 12 October 2026; check the current NOTAM list for which airports and segments apply.
Common questions
How do I correct altitudes for cold temperature?
Take the height of each published altitude above the airport (or the altimeter setting source), then use the reported airport temperature in the ICAO formula or the ICAO table to find how much to add. Round up and fly that on the altimeter. At a 1,000 ft airport and −25 °C, a 3,000 ft FAF is 2,000 ft above the field, the correction is 308 ft and you fly 3,400 ft.
What is the 4% rule for cold temperature?
Add 4% of the height above the airport for every 10 °C the airport is below the standard (ISA) temperature. At a 1,000 ft airport ISA is 13.0 °C, so −25 °C is 38.0 °C below. For a height of 2,000 ft that is 2,000 × 4% × 3.8 = 304 ft, close to the 308 ft from the ICAO formula. It is a quick cross-check, not a replacement for the formula or table.
What is a Cold Temperature Airport?
In the United States the FAA lists Cold Temperature Airports (CTA). Their approach charts show a snowflake symbol and a temperature. When the reported airport temperature is at or below that figure, pilots correct the altitudes in the marked segments (intermediate, final, missed approach or all). Tell ATC when you fly a corrected altitude in the intermediate or missed approach segment. Check the current FAA list and the AIM.
Which altitudes should I correct in cold weather?
The minimum altitudes that keep you clear of terrain: initial and intermediate approach altitudes, the FAF, step-down fixes, the MDA or DA and the missed approach altitude. Do not correct altitudes ATC gives you on radar vectors, and do not change the altimeter setting itself. Many operators and states set their own rules, so follow your AIP and operator procedures.
Why is the correction bigger for higher altitudes?
The error builds up through every layer of cold air between you and the altimeter setting source, so it grows with height above that source. At −25 °C on a 1,000 ft airport, an MDA 500 ft above the field needs 77 ft added, but an altitude 3,000 ft above needs 464 ft. Only the height above the source counts, not the height above sea level.
Do I need to correct altitudes when it is hot?
No. When the air is warmer than standard you are higher than the altimeter shows, so published altitudes still keep you clear of terrain. This calculator shows no correction when the airport is at or above ISA. Warm air can still matter for some baro-VNAV approaches, which publish their own temperature limits.
Related calculators
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.