Horsepower Calculator
Estimate your engine's flywheel horsepower from your quarter-mile ET, trap speed, and vehicle weight using proven drag-racing formulas. Enter what you know — ET, trap speed, or both.
Bottom line: this horsepower calculator estimates flywheel HP from your quarter-mile ET and trap speed using the proven Roger Huntington drag formulas. Trap speed is the more reliable input — it is far less sensitive to traction than ET — so measure a clean run and let the trap-based number lead.
How to Use the Calculator
- Enter your vehicle's race weight in pounds (including fuel and driver)
- Enter your 1/4-mile ET in seconds, your trap speed in mph, or both
- The calculator returns an estimated flywheel horsepower figure; supply both ET and trap and it averages the two
The Drag-Racing Formulas
This calculator inverts the classic Roger Huntington quarter-mile equations to solve for horsepower from your run data and weight:
- HP = Weight × (5.825 / ET)³ — flywheel horsepower from elapsed time
- HP = Weight × (Trap ÷ 234)³ — flywheel horsepower from trap speed
When you supply both ET and trap speed, each estimate is shown separately and averaged for the headline figure.
Flywheel vs. Wheel Horsepower
These formulas estimate flywheel (crankshaft) horsepower — the power the engine makes before the drivetrain takes its cut. A chassis dyno instead reads wheel horsepower, which is lower:
- Manual or automatic RWD: expect roughly 10–15% drivetrain loss
- All-wheel drive: expect around 15% or more
- To approximate wheel HP, multiply the flywheel estimate by about 0.85–0.88
Why These Are Estimates
The formulas assume a clean, well-hooked-up run. A poor launch, spinning tires, hot or high-altitude air, or an off weight figure will all skew the result. ET is especially traction-sensitive — a spun launch inflates ET and understates power. That is why real GPS timing is so valuable: accurate ET and trap data feed directly into a far more trustworthy estimate.
Rough HP by Quarter-Mile ET
Approximate flywheel horsepower ranges for a ~3,500 lb car. Real numbers vary with traction, launch, weather, and drivetrain — use this as a sanity check only.
| Quarter-Mile ET | Approx. HP (~3,500 lb) | Typical Examples |
|---|---|---|
| ~14s | 200–260 hp | Stock sport sedans, warm hatchbacks |
| ~13s | 260–330 hp | Stock sports cars, tuned 4-cylinders |
| ~12s | 330–430 hp | V8 muscle, hot turbo builds |
| ~11s | 430–560 hp | High-boost, supercharged, light modifications |
| ~10s | 560–720 hp | Big-boost builds, drag-prepped setups |
Verify Your Real Numbers with GPS
A calculator is only as good as the ET and trap you feed it. FastTrack measures quarter-mile ET within ±0.04 seconds and trap speed within ±0.3 mph using GPS Doppler velocity fused with a 100Hz accelerometer — Dragy-class accuracy for free. Run a clean quarter mile, then plug the numbers straight into this calculator.
Download FastTrack Free on the App Store
Quarter Mile Calculator | Power-to-Weight Calculator | Quarter Mile Times by Vehicle | GPS Timing
Frequently Asked Questions
How accurate is a horsepower calculator?
An ET/trap-based estimate is usually within 10–15% of a real dyno pull for a clean run. It cannot precisely account for traction, launch quality, weather, altitude, or drivetrain loss, so treat it as a ballpark. Trap-speed-based estimates track real power more closely than ET-based ones.
Should I use ET or trap speed to estimate HP?
Trap speed. ET is heavily influenced by traction and launch technique — a bad launch or slippery surface inflates ET and understates power. Trap speed is far less traction-sensitive, so it tracks true engine output much more closely. If you have both, lead with the trap-based figure.
Is this flywheel or wheel horsepower?
Flywheel (crankshaft) horsepower — the power before drivetrain losses. Wheel horsepower, what a chassis dyno reads, is lower: roughly 10–15% loss for a manual or automatic RWD drivetrain and around 15% or more for AWD. To approximate wheel HP, multiply the flywheel estimate by about 0.85–0.88.
Why is my calculated HP different from my dyno?
The calculator estimates flywheel HP while most dynos read wheel HP; your race weight or trap speed may be off; a poor launch or spinning tires produces a slower run than your power warrants; and weather, altitude, and dyno correction factors all shift numbers. Use it as a sanity check, not a replacement for a dyno.
How do I measure my quarter mile ET and trap speed?
Use FastTrack — it is free and measures quarter-mile ET within ±0.04 seconds and trap speed within ±0.3 mph using GPS Doppler velocity fused with a 100Hz accelerometer. Run a clean quarter mile on a safe, legal surface, then plug the ET and trap speed straight into this calculator.