Calculate horsepower loss and remaining engine power at altitude, recover sea-level power, or solve altitude using the 3% rule, ISA model, HP, kW, ft, or m.

Use a sea-level reference for the same engine and operating condition.

Model estimate only. Weather, intake temperature, engine controls and forced induction can change actual power. These models are not manufacturer ratings, dyno correction standards or aircraft performance data.

HP Loss at Altitude Formula

The following two example problems outline the steps and information needed to calculate the HP Loss at Altitude.

HPL = EP × A / 1000 × .03

Variables:

  • HPL is the HP Loss at Altitude (HP loss)
  • EP is the original engine power (HP) 
  • A is the total altitude (ft) 

For the 3%-per-1,000-ft linear scenario, multiply the sea-level reference power by altitude in feet divided by 1,000, then by0.03. This is an assumed model rather than a universal engine rating. The separate dry-air ISA proxy assumes power proportional to standard atmospheric density and is limited to0–11,000m model altitude; weather and forced induction can change actual output.

How to Calculate HP Loss at Altitude?

The following steps outline how to calculate the HP Loss at Altitude.

  1. First, determine the original engine power (HP). 
  2. Next, determine the total altitude (ft). 
  3. Next, gather the formula from above = HPL = EP * A/1000 *.03.
  4. Finally, calculate the HP Loss at Altitude.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

original engine power (HP) = 300

total altitude (ft) = 5000

HPL = EP * A/1000 *.03 = ?