Performance
Predict quarter-mile ET and trap MPH using the Wallace and Fox formulas from vehicle weight and horsepower. The drag-strip standard for estimating performance before track day.
A quarter-mile calculator predicts elapsed time and trap speed from weight and horsepower, or back-calculates horsepower from your track slip. It uses common Wallace-style correlations racers have used for decades to bench-race combinations before spending on parts.
Use it to see whether 450 HP should run mid-11s at your race weight, or to estimate power from a pass when the dyno is unavailable. Tow vehicles and daily drivers use the same math to understand why weight reduction matters as much as power for ET.
Results are theoretical — traction, weather, gearing, and driver skill move real times. Pair with horsepower and 0–60 tools for a full acceleration picture.
Enter race weight with driver and fuel. Curb weight alone makes ET look quicker than reality.
Use RWHP for honest predictions; crank HP makes the car look faster on paper.
“HP from ET” and “HP from trap” modes answer different questions — sloppy launches hurt ET more than trap; use trap when the sixty-foot was bad but top-end was strong.
Prepped track and slicks can run quicker than the estimate; cold street tires and wheelspin run slower.
Wallace-style estimates (common bench-race math):
ET (sec) ≈ 5.825 × (Weight ÷ HP)1/3
Trap (MPH) ≈ 234 × (HP ÷ Weight)1/3
Example: 3,500 lb, 450 HP → ET ≈ 5.825 × (3500/450)1/3 ≈ 11.5 sec; Trap ≈ 234 × (450/3500)1/3 ≈ 118 MPH.
To solve for HP from ET: HP ≈ Weight ÷ (ET ÷ 5.825)³
ET ≈ 5.825 × (Weight ÷ HP)1/3. Trap ≈ 234 × (HP ÷ Weight)1/3.
Example: 3,500 lb, 450 HP → ET ≈ 11.5 sec, trap ≈ 118 MPH.
Solve for HP from ET: HP ≈ Weight ÷ (ET ÷ 5.825)³. High elevation and headwind raise ET without changing true engine power.
Enter 4,443 lb and 485 hp (2021 Challenger Scat Pack, Car and Driver as-tested weight and rated power). The predictor lands near mid-11-second ET with trap around 114 mph — in the ballpark of their 12.2 @ 114 street test, with gap for tires, weather, and RWHP versus crank rating.
If your car weighs 3,600 lb and runs a 12.8-second quarter-mile at the track, the “HP from ET” mode estimates equivalent power. Compare that to dyno RWHP — large differences usually mean traction limits, converter slip, or weather, not a broken calculator.
Car and Driver tested a 2022 Subaru BRZ at 2,815 lb and 228 hp, recording a 14.0-second quarter-mile at 99.5 mph. Lower weight and moderate power still follow the same ET/HP math — handy for sanity-checking BRZ/GR86-style builds.
The quarter-mile predictor assumes reasonable traction and a clean launch. If your ET is slower than predicted while trap speed looks strong, the story is almost always in the first 60 feet — wheelspin, bogged converter, or a soft shift — not missing horsepower.
Street tires on a cold public lane cannot match prepped drag-strip resin and slicks. Conversely, entering brochure crank HP while the car puts down less at the wheels makes the math look slower than your pass — or faster if you accidentally used RWHP with crank-rated power.
Headwind, altitude, and heat change true engine output between test days. Log race weight with driver and fuel every pass; use trap-speed mode in the horsepower calculator to back-solve power when ET is messy but MPH through the traps is honest.
Use race weight — vehicle, driver, tools, and fuel as raced. Curb weight alone is optimistic by 150–250 lb for most street passes.
That pattern often means poor launch / high sixty-foot but strong top-end (aero, power, or gearing). Trap and ET solve different parts of the pass.
Yes. Thin air reduces power; many tracks see slower ET and lower trap at high elevation unless forced induction compensates. Compare runs at similar DA when possible.
Pair this calculator with these related tools in the garage — same session, no signup.