Quarter Mile Calculator
Estimate your car’s quarter-mile elapsed time and trap speed from weight and horsepower using proven racing formulas.
Quarter Mile ET Calculator
Weight + HP → ET + Trap Speed
How It Works
The Elapsed Time (ET) formula by Roger Huntington uses the cube root of the power-to-weight ratio. It is a widely cited empirical formula for stock street cars running on slicks or radials.
How to Use This Calculator
- Enter the vehicle's total weight (with driver) in lb or kg.
- Select the weight unit.
- Enter flywheel horsepower (crank HP from dyno or manufacturer spec).
- Click Calculate — see estimated ET and trap speed.
- Note: results are estimates — real ET depends on traction, launch, and gearing.
Worked Example
Reference Table
| HP/Weight Ratio | ET (est.) | Trap MPH | Example Vehicle |
|---|---|---|---|
| 0.05 (very slow) | 16.2 s | 79 mph | Old economy car |
| 0.10 | 12.9 s | 99 mph | Mild street car |
| 0.15 | 11.2 s | 113 mph | Sport sedan |
| 0.20 | 10.2 s | 124 mph | Hot hatch |
| 0.30 | 8.9 s | 142 mph | Supercar |
| 0.50 | 7.4 s | 167 mph | Drag-built race car |
Frequently Asked Questions
How accurate is the quarter-mile formula for modified cars?
The Huntington formula works best for stock-class cars with good traction. Highly modified cars with drag radials, nitrous, or turbo systems may run 0.3–0.7 seconds faster than predicted due to superior launch and power delivery.
What weight should I use — curb weight or race weight?
Use race weight: curb weight plus driver (approx. 80 kg / 175 lb) plus fuel. A full tank of fuel adds roughly 30–45 kg. Strip unnecessary weight from the interior for a more accurate strip-ready estimate.
Why does flywheel HP overestimate real-world ET?
Drivetrain losses (8–18% for manual, 12–25% for auto) mean wheel HP is lower. Some racers use wheel HP in the formula for a closer real-world estimate.
Can this formula be used for km/h and kilometres?
The formula constants are tuned for Imperial units (lb, HP, mph). Convert the trap speed: mph × 1.60934 = km/h. For kilometres, 402.34 m = 1/4 mile.
