The Horsepower Quarter Mile Calculator takes crank horsepower, race weight, and drivetrain layout, and returns the elapsed time and trap speed the car should run across 1,320 feet.
Estimate Quarter Mile ET and Trap Speed From Horsepower and Weight
Enter crank horsepower, race weight, and drivetrain layout, and this quarter mile calculator returns an elapsed time for 1,320 feet, a trap speed, an eighth mile split, and a 60-foot estimate. It is aimed at people planning a build, comparing two setups, or checking a time slip against what the car should run.
What Common Power and Weight Combinations Run
These are rear-wheel-drive figures straight from the tool’s math.
| Power | Weight | ET | Trap speed |
|---|---|---|---|
| 200 HP | 2,800 lb | 14.04 s | 97.1 MPH |
| 300 HP | 3,000 lb | 12.55 s | 108.6 MPH |
| 300 HP | 3,500 lb | 13.21 s | 103.2 MPH |
| 400 HP | 3,500 lb | 12.00 s | 113.6 MPH |
| 500 HP | 3,500 lb | 11.14 s | 122.3 MPH |
| 600 HP | 3,800 lb | 10.78 s | 126.5 MPH |
| 700 HP | 4,000 lb | 10.41 s | 130.9 MPH |
Notice how little the ET moves at the top. Going from 400 to 500 HP at the same weight buys under a second. That is the cube root at work. Power has to rise by roughly 40 percent to cut ET by 10 percent.
The Formulas and How to Run Them Backwards
Both equations come from Patrick Hale, who refitted the older drag racing constants using more modern data. Weight is in pounds and power is at the crank. $$ET = 5.825 \times \left(\frac{W}{HP}\right)^{1/3} \qquad MPH = 234 \times \left(\frac{HP}{W}\right)^{1/3}$$
Both work in reverse, which is how a lot of people estimate power without a dyno. $$HP = W \times \left(\frac{MPH}{234}\right)^{3} \qquad HP = W \times \left(\frac{5.825}{ET}\right)^{3}$$
Of the two, trap speed is the better estimator. Trap speed reflects the energy the car actually built over the run. ET absorbs launch mistakes and wheelspin, so a bad 60-foot makes the car look down on power when it is not.
Metric entries are converted before the math runs. Kilograms become pounds at 2.2046 and kilowatts become horsepower at 1.3410. The equations themselves are imperial.
Why This Reads Quicker Than Other Quarter Mile Calculators
Three constant sets are in common use, and they do not agree. Here is the same 3,500 lb car with 400 HP through all three.
| Formula | ET constant | ET | Trap speed |
|---|---|---|---|
| Hale (used here) | 5.825 | 12.00 s | 113.6 MPH |
| Fox | 6.269 | 12.92 s | 111.6 MPH |
| Huntington | 6.290 | 12.96 s | 108.7 MPH |
Nearly a full second separates Hale from Huntington. Trap speed stays within a few miles per hour across all three, which is another reason trap is the more reliable figure.
Hale’s numbers assume a good launch on a prepared surface. If you run street tires on a cold track, expect the real ET to land closer to the Huntington column. Huntington’s constants came from 1950s data. Fox published his in 1973 in the American Journal of Physics.
Enter Crank Power, Not Wheel Power
Hale’s formulas were built around flywheel horsepower. The input here is labelled crank power for that reason.
Put a chassis dyno number in and the result comes out slow. A 3,500 lb car with 400 wheel horsepower is closer to 470 at the crank with a 15 percent loss. That changes the prediction from 12.00 seconds to about 11.37.
Race weight matters just as much. Use the weight of the car with driver and the fuel you will actually run, not the curb weight from a brochure.
What the Supporting Cards Assume
The main ET and trap figures are Hale’s. Everything else on the page is this calculator’s own layer, and none of it traces to a published source.
The drivetrain setting multiplies ET by 1.00 for RWD, 1.05 for FWD, and 0.95 for AWD. Trap speed is deliberately left alone, because trap tracks power-to-weight rather than how well the car launches.
The 60-foot card takes a fixed share of total ET: 16 percent for RWD, 18 percent for FWD, and 14.5 percent for AWD. The eighth mile card uses fixed proportions too, at 64 percent of the ET and 80 percent of the trap speed.
The 0-60 row deserves a warning. It assumes acceleration stays constant for the whole run, so it just scales ET by the ratio of 60 mph to trap speed. Real cars pull hardest off the line and taper as speed climbs, so they reach 60 sooner than a straight-line average suggests. Treat that row as a rough upper bound, not a 0-60 prediction.
Inputs stop at 500 lb and 10 HP, or 226.8 kg and 7.46 kW. Below that the calculation halts. There is no upper limit, and no input for traction, gearing, tires, converter, altitude, or air density.
Quarter Mile Estimate Questions
How accurate is a quarter mile calculator?
For a naturally aspirated car with decent traction, expect a few tenths either way. Turbo cars, sticky tires, and bad launches all move ET more than the formula can see. Trap speed predictions hold up better than ET.
Why did my car trap the predicted speed but run a slower ET?
That is the classic traction signature. Trap speed says the power is there. A slow ET with a correct trap means the time went missing in the first 60 feet, usually to wheelspin or a soft launch.
How much horsepower do I need for an 11 second quarter?
Rearrange the ET formula. For an 11.00 second pass in a 3,500 lb car, you need 3,500 × (5.825 ÷ 11.00)³, which is about 520 crank horsepower under Hale’s constants.
Does the calculator account for gearing or a torque converter?
No. Neither is an input. Two cars with the same power and weight get the same answer here, even though gearing, converter stall, and shift points can separate them by several tenths in reality.
Should I trust the AWD number?
Treat it as directional. All-wheel drive really does launch better, and the tool credits it 5 percent, but that figure is an assumption rather than a measured correction. A well-hooked AWD car can beat it, and a poorly geared one will not reach it.