Cold Weather Altimetry Correction Calculator
ICAO cold-temperature corrections: how many feet to add to published approach altitudes when the air is colder than ISA.
Rule of thumb: about 4% of height above the station per 10 °C below ISA. At −25 °C surface and 1,500 ft above the station the altimeter overstates height by ~180 ft — terrain doesn't grade on a curve.
Formula
⚠️ For flight planning and education only — always verify against your aircraft's POH/AFM, official weather sources and certified instruments. Not for primary navigation or airworthiness decisions.
ICAO cold-temperature corrections: how many feet to add to published approach altitudes when the air is colder than ISA.
About Cold Weather Altimetry Correction Calculator
Cold air shrinks the atmosphere, and an altimeter calibrated for ISA happily reports heights that no longer exist. This calculator implements the ICAO Doc 8168 cold-temperature correction — the same formula behind the published correction tables — returning the feet to add to a procedure altitude given height above the reporting station and surface temperature, plus the sobering 'true height if you don't' figure.
How to use Cold Weather Altimetry Correction Calculator
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula ΔH = H_above-station × (−ISA dev) / (273 + t₀ − 0.5·L·H); L = 0.0065 K/m substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Cold Weather Altimetry Correction Calculator?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula ΔH = H_above-station × (−ISA dev) / (273 + t₀ − 0.5·L·H); L = 0.0065 K/m with sources cited on the page
- ✓Rule of thumb: about 4% of height above the station per 10 °C below ISA. At −25 °C surface and 1,500 ft above the station the altimeter overstates height by ~180 ft — terrain doesn't grade on a curve.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
When are cold-temperature corrections legally required?+
In the US, at the FAA's published Cold Temperature Restricted Airports (snowflake symbol on the approach chart) when at or below the published trigger temperature — corrections are then mandatory on designated segments, with ATC advised. Elsewhere, PANS-OPS states and many operators' SOPs require corrections below 0 °C on procedures near terrain. Operator and state rules govern.
How big can the error get?+
Roughly 4% of your height above the altimeter source per 10 °C below ISA. At −40 °C surface (≈55 °C below ISA at low elevation) and 2,000 ft above the station, the altimeter overstates height by well over 400 ft — more than an entire approach segment's obstacle margin in mountainous terrain.
Which altitudes on an approach do I correct?+
Per FAA guidance at CTA airports: the segments listed for that airport (often intermediate, FAF/glideslope intercept, MDA/DA, and missed approach). Under full PANS-OPS practice, all minimum altitudes from initial approach through missed approach are corrected. Never correct assigned vectors' altitudes without telling ATC — separation is built on uncorrected numbers.
Does GPS/baro-VNAV guidance fix this automatically?+
LNAV/VNAV minima flown with baro-VNAV are temperature-limited for exactly this reason — check the chart's temperature limits box. SBAS (LPV) vertical guidance is geometric and immune to temperature error, but the published minimum altitudes you must still respect remain barometric and still need correcting.
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