Altitude Power Loss Calculator (Naturally Aspirated Engines)
How much power a naturally aspirated engine loses at altitude and in warm air, from the standard atmosphere and your air temperature.
Results
The dashed line marks the value you entered.
What this tool does
An engine without a turbo or supercharger burns only the air it can breathe in, so its power follows the density of the air. Thinner air at altitude costs roughly 9 % of power at 1,000 m and 18 % at 2,000 m on a standard day, and warm air is thinner too: each 10 °C warmer costs about 3 %. The pressure comes from the standard atmosphere (ISA), valid up to 11 km; enter the real air temperature where you are. Turbo engines hold their power to a higher altitude, and modern engine management keeps the mixture right, so measured losses can differ — treat this as a first-order estimate.
Formula
p = 101325 (1 − 0.0065 h ÷ 288.15)^5.25588 · ρ ÷ ρ₀ = (p ÷ 101325) × (288.15 ÷ T) · P = P₀ × ρ ÷ ρ₀
Variables
| Symbol | Meaning | Unit |
|---|---|---|
pw | Engine power at sea level (any unit) | — |
al | Altitude | m |
tc | Temperature | °C |
PA | Power at that altitude | — |
PL | Power lost (negative means gained) | % |
DS | Air density as a share of the standard sea-level value | % |
PK | Air pressure at that altitude (standard atmosphere) | kPa |
IT | Standard-atmosphere temperature at that altitude | °C |
Worked example
- Engine power at sea level (any unit)100
- Altitude2000 m
- Temperature2 °C
- Power at that altitude82.2
- Power lost (negative means gained)17.8 %
- Air density as a share of the standard sea-level value82.2 %
- Air pressure at that altitude (standard atmosphere)79.50 kPa
- Standard-atmosphere temperature at that altitude2.0 °C
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.