Density Altitude Calculator (Metric / hPa)
Full-metric density altitude for pilots flying QNH in hectopascals and elevations in metres — ICAO units, no inches of mercury anywhere.
8.23 m per hPa and 36.21 m per °C are the metric twins of the familiar 1,000 ft/inHg and 118.8 ft/°C rules. ICAO ISA lapse rate: 6.5 °C per 1,000 m.
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.
Full-metric density altitude for pilots flying QNH in hectopascals and elevations in metres — ICAO units, no inches of mercury anywhere.
About Density Altitude Calculator (Metric / hPa)
Most density-altitude calculators online assume inches of mercury and feet — useless friction if your AIP, METARs and charts speak hectopascals and metres. This tool is metric end to end: QNH in hPa, elevation in metres, lapse rate at the ICAO 6.5 °C/km, with the conversion factors (8.23 m per hPa, 36.21 m per °C) shown in the worked example rather than hidden. A US-unit toggle is one click away when you need to compare.
How to use Density Altitude Calculator (Metric / hPa)
- 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 PA(m) = elev + (1013.25 − QNH) × 8.23; ISA = 15 − 6.5·PA(km); DA(m) = PA + 36.21 × (OAT − ISA) substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Density Altitude Calculator (Metric / hPa)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula PA(m) = elev + (1013.25 − QNH) × 8.23; ISA = 15 − 6.5·PA(km); DA(m) = PA + 36.21 × (OAT − ISA) with sources cited on the page
- ✓8.23 m per hPa and 36.21 m per °C are the metric twins of the familiar 1,000 ft/inHg and 118.8 ft/°C rules. ICAO ISA lapse rate: 6.5 °C per 1,000 m.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
How do I convert QNH in hPa to pressure altitude?+
Each hectopascal away from the standard 1013.25 hPa is worth about 8.23 m (27 ft) of pressure altitude. QNH below standard puts pressure altitude above field elevation; QNH above standard puts it below. This tool computes PA = elevation + (1013.25 − QNH) × 8.23 and shows the substitution explicitly.
Why 36.21 metres per degree Celsius?+
It is the metric equivalent of the FAA's 118.8 ft/°C: the density-altitude correction per degree of deviation from ISA temperature. Multiply the ISA deviation at your pressure altitude by 36.21 m and add it to pressure altitude — exactly what the result panel's worked example walks through with your numbers.
Does this match what my European flight computer gives?+
Within the tolerance of the underlying approximations, yes — both implement the ICAO standard atmosphere with the linear temperature correction. Small differences (tens of metres) arise from rounding the hPa-to-metres factor or using exact barometric formulas instead of the linear correction. For performance planning those differences are immaterial.
When does QFE vs QNH matter for this calculation?+
Use QNH (sea-level-referenced) with the field's elevation, as this calculator does. If you only have QFE (the field-level pressure), either convert it — QNH ≈ QFE + elevation/8.23 m·hPa⁻¹ — or use a station-pressure-based tool. Mixing QFE with field elevation here would double-count the airport's height.
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