Convert net horsepower to gross horsepower, or wheel hp to crank hp, using a typical difference or your own percentage, with results in hp, kW or PS.
Formula
Lower → Higher Power:
HPgross = HPnet ÷ (1 − L)
Higher → Lower Power:
HPnet = HPgross × (1 − L)
From measured loss:
HPgross = HPnet + HPloss
In these algebraic formulas, the higher and lower powers refer to the selected comparison: engine gross versus engine net, or crank versus wheel. L is the supplied difference as a fraction of the higher power; HPloss is a supplied fixed difference in the same power unit. These are assumed relationships, not a standardized conversion between SAE ratings.
Interpretation
SAE net and gross are engine power ratings under specified test configurations; net engine power is not wheel power. Wheel/crank comparisons instead concern drivetrain power loss. The calculator keeps these comparisons separate. Pick a typical rule-of-thumb difference, or supply one supported by compatible measurements.
The percentages below are illustrative drivetrain-loss assumptions, not validated typical ranges or conversion factors. Vehicle layout alone does not establish a loss percentage:
- FWD manual: ~10%
- FWD automatic: ~12%
- RWD manual: ~15%
- RWD automatic: ~17–18%
- AWD manual: ~20–22%
- AWD automatic: ~22–25%
Check measurement basis, correction conditions and units before comparing powers. A percentage alone cannot diagnose a dyno mismatch or establish whether a drivetrain is standard.
Illustrative Wheel-to-Crank Table
The following rounded examples use assumed losses of 15%, 18% and 22%; they do not convert SAE net engine power to SAE gross power.
| Net (whp) | 15% loss | 18% loss | 22% loss |
|---|---|---|---|
| 150 | 176 hp | 183 hp | 192 hp |
| 250 | 294 hp | 305 hp | 321 hp |
| 350 | 412 hp | 427 hp | 449 hp |
| 450 | 529 hp | 549 hp | 577 hp |
| 550 | 647 hp | 671 hp | 705 hp |
FAQ
Is drivetrain loss a fixed percentage or a fixed number of horsepower?
Both are simplified models. Loss depends on operating and measurement conditions. A coast-down figure is not automatically the loaded drivetrain loss and does not guarantee a precise crank-power estimate. Use a supplied fixed difference only when its measurement basis is applicable.
Why doesn’t my dyno number match the factory horsepower rating minus 15%?
Factory engine ratings and chassis-dyno wheel readings have different measurement bases. Equipment, calibration, correction conditions, tire behavior, drivetrain temperature and operating conditions can change the comparison; subtracting a universal 15% is not justified.
What’s the difference between gross, net, and SAE certified horsepower?
SAE J1349 addresses as-installed net engine power; SAE J1995 addresses gross engine power. J2723 certification can certify ratings under either applicable power test. These engine ratings are distinct from chassis-dyno wheel power.
Can I use kW or PS instead of hp?
Yes. Select one shared power unit for all power inputs. Results use that unit, with mechanical hp, kW and metric horsepower (PS) equivalents in Calculation details. Mechanical hp and PS are distinct units; NIST conversion factors distinguish them.
