Estimate density-corrected power from measured mechanical hp or kW, station pressure, temperature and humidity. This calculator uses a moist-air density ratio, not an SAE, DIN or STD dyno correction standard.

Estimate corrected power from measured power and test-day conditions.

Air-density estimate only. Reference: 101.325 kPa, 15ยฐC, dry air. This does not implement SAE, DIN or STD dyno standards.

Supported range: โˆ’30 to 35ยฐC (โˆ’22 to 95ยฐF). Humidity is relative to liquid water.

Use absolute pressure at the test site, not sea-level-adjusted weather pressure.

Dyno Correction Formula

The following air-density relationship is used to estimate corrected horsepower (corrected to 101.325 kPa, 59ยฐF (15ยฐC), dry air):

CHP & = HP ร— (ฯstd) / (ฯโ‚œโ‚‘โ‚›โ‚œ) \ ฯ & = (Pd) / (Rd T) + (Pแตฅ) / (Rแตฅ T)

Variables:

  • CHP is the corrected horsepower (HP)
  • HP is the horsepower measured on the dyno (HP)
  • T is the intake/ambient air temperature during the test (converted to absolute temperature, K)
  • BP is the station barometric pressure during the test (converted to Pa)
  • H is the relative humidity during the test (%)
  • ฯstd is the air density at the reference conditions (101.325 kPa, 59ยฐF / 15ยฐC, 0% RH)
  • ฯtest is the air density during the test computed from BP, T, and H

To estimate corrected horsepower, multiply the measured horsepower by the ratio of standard air density to the test-day air density. Note: many dynamometers also offer specific standard corrections (e.g., SAE, DIN, STD). If you need compliance with a particular standard, use the correction method specified by your dyno or rulebook.

What is Dyno Correction?

Dyno correction is the process of adjusting the horsepower measured by a dynamometer (dyno) to account for variations in atmospheric conditions. Since engine output can be affected by temperature, air pressure, and humidity (which change the oxygen available for combustion), applying a consistent correction method helps make horsepower readings more comparable across different conditions. Certified comparisons and racing compliance require the method specified by the dyno or rulebook; this simplified density estimate does not establish compliance.

How to Calculate Corrected Horsepower?

The following steps outline how to calculate the Corrected Horsepower.

  1. First, determine the horsepower measured on the dyno (HP).
  2. Next, determine the temperature at the time of the test (T).
  3. Next, determine the station barometric pressure at the time of the test (BP).
  4. Next, determine the relative humidity at the time of the test (H) in percent (%).
  5. Compute the test-day air density (ฯtest) from BP, T, and H, and the reference air density (ฯstd) from the chosen standard conditions.
  6. Finally, calculate the corrected horsepower: CHP = HP ร— (ฯstd / ฯtest).
  7. 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.

horsepower measured on the dyno (HP) = 300 HP

temperature at the time of the test (T) = 75 ยฐF

barometric pressure at the time of the test (BP) = 29.92 inHg

relative humidity at the time of the test (H) = 50%

Using the moist-air density correction to 101.325 kPa, 59ยฐF (15ยฐC), and dry air, the estimated corrected power is approximately 311.0 mechanical hp. The vapor-pressure approximation is supported from โˆ’30 to 35ยฐC, with relative humidity defined over liquid water. See UCARโ€™s Bolton humidity equations and Dynojetโ€™s correction-standard descriptions.