Quarter Mile Calculator
Quarter mile calculator estimates ET and trap speed from horsepower and weight with Hale, Fox or Huntington, plus the hp needed for a target time.
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How the Quarter Mile Calculator Formula Works
A car's quarter mile time depends mostly on how much power it has for its weight. The classic formulas say the elapsed time is a constant times the cube root of the weight divided by the horsepower, and the trap speed is another constant times the cube root of the horsepower divided by the weight.
There are three common sets of constants. Hale uses 5.825 for time and 234 for speed, Fox 6.269 and 230, and Huntington 6.290 and 224. Weight is in pounds including the driver and power is flywheel horsepower. For a 3,200 pound car with 400 horsepower the ratio is 8, its cube root is 2, so the Hale time is 5.825 × 2 = 11.65 seconds and the speed is 234 × 0.5 = 117 miles an hour.
Run the other way, the horsepower needed for a target time is weight x (constant / time) cubed. The calculator also gives one-eighth mile figures, the time divided by 1.56 and the speed divided by 1.25. These are first-order estimates: tires, traction, gearing, weather and the driver all move the real result.
ET = c × (weight / horsepower)1/3; trap speed = k × (horsepower / weight)1/3; Hale c = 5.825, k = 234- horsepowerhpFlywheel (crank) horsepower.
- weightlb or kg3200Race weight including the driver.
- formulaHale, Fox, HuntingtonhaleWhich set of constants to use.
- target ETsecondsFor the power-needed mode.
- horsepower
- hp
- Flywheel (crank) horsepower.
- weight
- lb or kg
- Race weight including the driver.
- formula
- Hale, Fox, Huntington
- Which set of constants to use.
- target ET
- seconds
- For the power-needed mode.
Using the Quarter Mile Calculator
Enter calculate
Choose from ET and speed from power and weight, Power needed for a target ET.
Enter formula
Choose from Hale, Fox, Huntington.
Enter weight with driver
Type the figure you already have, then press Calculate.
Enter weight unit
Choose from Pounds, Kilograms.
Enter flywheel horsepower
Type the figure you already have, then press Calculate.
Enter target quarter mile et (seconds)
Any value between 4 and 30.
Read the result
Press Calculate to update the result. Until you do, the last result is dimmed and marked as out of date, so you always know which numbers belong to the values in the boxes.
A Real Worked Example
A car weighs 3,200 pounds with the driver and makes 400 flywheel horsepower. The weight to power ratio is 3,200 / 400 = 8, and its cube root is exactly 2.
With the Hale constants the ET is 5.825 × 2 = 11.65 seconds, and the trap speed is 234 × 0.5 = 117 mph, which is 188.3 km/h. The eighth mile figures are 7.47 seconds at 93.6 mph.
The same car with the Fox formula
Switch to Fox. The ET is 6.269 × 2 = 12.54 seconds and the trap speed is 230 × 0.5 = 115 mph.
The eighth mile figures are 8.04 seconds at 92.0 mph. Fox is slower than Hale, so comparing the formulas gives a range.
Huntington, 500 hp at 3,200 lb
With 500 horsepower the weight to power ratio is 6.4, with a cube root of 1.857. Huntington gives 6.290 × 1.857 = 11.68 seconds at 224 × 0.5385 = 120.6 mph.
That is 1.0 hp for every 6.4 pounds, or 0.156 hp per pound.
Metric: 1,400 kg and 300 hp
Choose kilograms and enter 1,400 and 300 hp. The weight is 3,086.5 pounds, a ratio of 10.29, with a cube root of 2.175.
The Hale ET is 12.67 seconds at 107.6 mph, which is 173.2 km/h.
Power needed for an 11 second pass, 3,200 lb
Choose power needed, a target of 11 seconds and a weight of 3,200 pounds. Power = weight x (5.825 / 11) cubed = 3,200 × 0.1485 = 475.2 hp.
That is 0.148 hp per pound, and the trap speed would be about 123.9 mph.
A 9.5 second target at 3,500 lb with Fox
Choose Fox, a target of 9.5 seconds and 3,500 pounds. Power = 3,500 × (6.269 / 9.5) cubed = 1,005.8 hp.
That is 0.287 hp per pound, and a trap speed of about 151.8 mph. Heavy cars need a lot of power for fast times.
700 hp, 3,400 lb
A 3,400 lb car with 700 hp has a ratio of 4.857, with a cube root of 1.693. The Hale ET is 5.825 × 1.693 = 9.86 seconds at 234 × 0.5907 = 138.2 mph.
That is 222.4 km/h, with an eighth mile of 6.32 seconds at 110.5 mph.
What Else to Know
How the Quarter Mile Calculator Works
The calculator estimates a quarter mile pass from two numbers: the power of the car and its weight with the driver. A car with more power for its weight is quicker, and the formulas say the effect follows a cube root.
It predicts the elapsed time and the trap speed, and converts them to one-eighth mile figures. In power-needed mode it works backwards from a target time to the horsepower required.
The quarter mile is 1,320 feet, 402 metres, the most common drag racing distance, according to Wikipedia.
A useful way to read the answer is as a range. The three formulas give 11.65, 12.54 and 12.58 seconds for the same car, so a realistic expectation sits within about a second of the middle. A well-prepared car on good tires may match Hale, while a street car on a rough surface may be closer to Huntington. The calculator shows all three so you can see where your own car is likely to fall.
The Three Formulas
Omni Calculator lists three sets of constants. Huntington's are 6.290 for time and 224 for speed, Fox's are 6.269 and 230, and Hale's are 5.825 and 234. Omni says Fox or Hale suit modern vehicles.
All three use the same shape: ET is a constant times the cube root of weight over power, and trap speed is a constant times the cube root of power over weight. The comparison table shows the three side by side for a 3,200 pound, 400 horsepower car.
Hale gives the quickest numbers, and the spread between them is a useful range.
Power, Weight and the Cube Root
Because of the cube root, doubling the power does not halve the ET. Doubling the power cuts the ET to about 79 percent of its value, since the cube root of two is 1.26. To drop a second or so you need a large change.
Only the ratio counts. Removing 10 percent of the weight has about the same effect as adding 11 percent more power. The ET and speed tables list common weight and power combinations.
The weight to horsepower ratio calculator on this site shows the ratio directly.
To see the effect, take the 3,200 pound car at 400 horsepower, 11.65 seconds. Adding 100 horsepower, to 500, gives 10.81 seconds, a gain of 0.84 seconds for 25 percent more power. Taking 320 pounds off the car instead, to 2,880, gives 11.25 seconds, a gain of 0.40 seconds. Each of these is a large change for a small gain in time, which is why fast times get expensive.
Flywheel Horsepower and Race Weight
The formulas expect flywheel, or crank, horsepower, the engine's output before the drivetrain takes its share. Wheel horsepower is lower, as Wikipedia notes, so using it will make the car look slower than it is.
Weight means race weight, the car plus the driver, fuel and anything else aboard. A 3,000 pound car with a 200 pound driver is 3,200 pounds.
If you only have a wheel horsepower figure, enter it and treat the answer as a pessimistic estimate.
Trap Speed and ET
Trap speed is the average speed over the final 66 feet before the finish line, according to Wikipedia. It follows the power closely, while ET also depends on the launch.
CalcHorsepower puts it this way: trap speed obeys the math, while ET rewards the launch. If your trap speed matches the calculator but your ET is slower, the gap is probably in the first 60 feet.
The power-needed mode can also work from a real trap speed or ET to estimate the power the car is making.
One-Eighth Mile Conversion
Many tracks run a one-eighth mile, 660 feet. A rough conversion divides the quarter mile ET by 1.56 and the speed by 1.25, the factors given by CalcHorsepower, and the other way round to go from eighth to quarter.
A 7.00 second eighth mile is about 10.92 seconds in the quarter mile. The conversion table shows six typical pairs.
The factors are approximations that vary with the car and the launch.
Limits of the Estimate
These are first-order approximations. Tires, track preparation, traction, gearing, shift points, weather, density altitude and the driver all change a real pass, and Omni Calculator notes that the formulas leave these out.
Typical accuracy is within a few tenths of a second under average conditions, but a poor launch can cost much more. The table of factors lists how each one affects ET and trap speed.
For the ratio on its own, see the weight to horsepower ratio calculator.
Reference Tables
| Term | Meaning |
|---|---|
| Elapsed time (ET) | The time from leaving the starting line to the finish line |
| Trap speed | The speed measured in the final 66 feet before the finish line |
| Reaction time | The time from the start signal to leaving the line; not part of ET |
| Flywheel (crank) horsepower | Engine power before drivetrain losses |
| Race weight | Car weight including driver and fuel |
| Density altitude | Air density expressed as an altitude; thinner air cuts engine power |
| Formula | Elapsed time (s) | Trap speed (mph) | Note |
|---|---|---|---|
| Hale | 5.825 × (W / P)1/3 | 234 × (P / W)1/3 | Often suits well-prepared, good-traction cars |
| Fox | 6.269 × (W / P)1/3 | 230 × (P / W)1/3 | Recommended for modern vehicles with Hale |
| Huntington | 6.290 × (W / P)1/3 | 224 × (P / W)1/3 | The oldest, slowest of the three |
| Formula | ET (s) | Trap speed (mph) | 1/8 mile ET (s) | 1/8 mile speed (mph) |
|---|---|---|---|---|
| Hale | 11.65 | 117.0 | 7.47 | 93.6 |
| Fox | 12.54 | 115.0 | 8.04 | 92.0 |
| Huntington | 12.58 | 112.0 | 8.06 | 89.6 |
| Weight (lb) | 200 hp | 300 hp | 400 hp | 500 hp | 700 hp | 1,000 hp |
|---|---|---|---|---|---|---|
| 2,500 | 13.52 | 11.81 | 10.73 | 9.96 | 8.90 | 7.91 |
| 3,000 | 14.37 | 12.55 | 11.40 | 10.58 | 9.46 | 8.40 |
| 3,200 | 14.68 | 12.82 | 11.65 | 10.81 | 9.67 | 8.58 |
| 3,500 | 15.12 | 13.21 | 12.00 | 11.14 | 9.96 | 8.84 |
| 4,000 | 15.81 | 13.81 | 12.55 | 11.65 | 10.41 | 9.25 |
| 4,500 | 16.44 | 14.37 | 13.05 | 12.12 | 10.83 | 9.62 |
| Weight (lb) | 200 hp | 300 hp | 400 hp | 500 hp | 700 hp | 1,000 hp |
|---|---|---|---|---|---|---|
| 2,500 | 100.8 | 115.4 | 127.0 | 136.8 | 153.1 | 172.4 |
| 3,000 | 94.9 | 108.6 | 119.5 | 128.8 | 144.1 | 162.2 |
| 3,200 | 92.9 | 106.3 | 117.0 | 126.0 | 141.0 | 158.8 |
| 3,500 | 90.1 | 103.2 | 113.6 | 122.3 | 136.8 | 154.1 |
| 4,000 | 86.2 | 98.7 | 108.6 | 117.0 | 130.9 | 147.4 |
| 4,500 | 82.9 | 94.9 | 104.4 | 112.5 | 125.8 | 141.7 |
| Target ET (s) | 3,000 lb | 3,500 lb | 4,000 lb | 4,500 lb |
|---|---|---|---|---|
| 14 | 216 | 252 | 288 | 324 |
| 13 | 270 | 315 | 360 | 405 |
| 12 | 343 | 400 | 458 | 515 |
| 11 | 445 | 520 | 594 | 668 |
| 10 | 593 | 692 | 791 | 889 |
| 9.5 | 692 | 807 | 922 | 1,037 |
| 9 | 813 | 949 | 1,084 | 1,220 |
| 8.5 | 965 | 1,126 | 1,287 | 1,448 |
| Quarter mile ET (s) | Eighth mile ET (s) | Quarter mile mph | Eighth mile mph |
|---|---|---|---|
| 14.00 | 8.97 | 98.0 | 78.4 |
| 13.00 | 8.33 | 105.0 | 84.0 |
| 12.00 | 7.69 | 114.0 | 91.2 |
| 11.00 | 7.05 | 124.0 | 99.2 |
| 10.00 | 6.41 | 136.0 | 108.8 |
| 9.00 | 5.77 | 150.0 | 120.0 |
| Quantity | Value |
|---|---|
| Quarter mile | 1,320 ft, 402 m |
| One-eighth mile | 660 ft, 201 m |
| Trap speed | Average speed over the last 66 ft (20 m) to the finish line |
| 1 mph | 1.609344 km/h |
| 1 lb | 0.45359237 kg |
| 1 hp | 745.7 W |
| Factor | Effect on ET | Effect on trap speed |
|---|---|---|
| Wheelspin or a poor launch | Slower ET | Little change |
| Tires and track prep | Large | Small |
| Weather and altitude | Slower with thin air | Lower |
| Using wheel horsepower with a crank formula | ET looks too slow | Speed looks too low |
| Forgetting the driver's weight | ET looks too fast | Speed looks too high |
| Gearing and shift points | Can cost tenths | Can cost mph |
Frequently Asked Questions About the Quarter Mile Calculator
How do I calculate quarter mile time from horsepower and weight?
Divide weight in pounds, with the driver, by horsepower, take the cube root and multiply by a constant. With the Hale constant, 3,200 lb at 400 hp is 5.825 × 81/3 = 11.65 seconds. Fox and Huntington use 6.269 and 6.290. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
What is the quarter mile ET formula?
ET = constant x (weight / horsepower)1/3. Omni Calculator lists Hale at 5.825, Fox at 6.269 and Huntington at 6.290. Weight is in pounds including the driver and power is in horsepower. The calculator lets you pick any of the three. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How do I calculate trap speed?
Trap speed = constant x (horsepower / weight)1/3, with 234 for Hale, 230 for Fox and 224 for Huntington. A 3,200 lb car with 400 hp traps at 234 × 0.5 = 117 mph by the Hale formula. Trap speed is the average over the last 66 feet. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How fast is a 400 hp car in the quarter mile?
At 3,200 lb, the Hale formula gives 11.65 seconds at 117 mph, Fox gives 12.54 at 115, and Huntington 12.58 at 112. A heavier car is slower. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How much horsepower for a 10 second quarter mile?
For a 3,500 lb car the Hale formula needs about 692 hp, and for 4,000 lb about 791 hp. The Fox formula needs more, about 862 for 3,500 lb. Use power-needed mode with your weight. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How much horsepower for an 11 second quarter mile?
At 3,200 lb the Hale formula needs about 475 hp and the Fox formula 592 hp. At 4,000 lb the Hale figure is 594. The needed-power table lists other times and weights. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How much horsepower for a 12 or 13 second quarter mile?
At 3,500 lb, Hale needs about 400 hp for 12 seconds and 315 hp for 13 seconds. Real cars need more if they cannot put the power down, so treat these as targets, not guarantees. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
Which formula is most accurate?
None is exact. Omni Calculator recommends Fox or Hale for modern vehicles, and says the formulas are a good first-order approximation that leaves out tires, aerodynamics and gearing. Hale tends to be quicker, so compare the three for a range. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
Why is my real ET different from the calculator?
Real passes depend on launch, traction, tires, gearing, weather and the driver, which the formula ignores. CalcHorsepower notes that trap speed follows the math while ET rewards the launch, and predictions are typically within a few tenths under average conditions. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
Should I use flywheel or wheel horsepower?
The formulas are written for flywheel (crank) horsepower, the engine's output before drivetrain losses. Wheel horsepower is lower, as Wikipedia notes. If you only know wheel horsepower, expect the calculator to give a slower ET than the car runs. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
Do I include the driver in the weight?
Yes. Use the race weight: the car plus the driver, fuel and anything else aboard. A 3,000 lb car with a 200 lb driver is 3,200 lb. Leaving out the driver makes the ET look too fast. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How do I convert quarter mile ET to eighth mile?
Divide the quarter mile ET by 1.56 and the trap speed by 1.25, the factors CalcHorsepower gives. An 11.65 second quarter mile is about 7.47 seconds in the eighth mile at 93.6 mph for a 117 mph trap speed. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How do I convert eighth mile ET to quarter mile?
Multiply the eighth mile ET by 1.56 and the speed by 1.25. CalcHorsepower's example is a 7.00 second eighth mile, which is about 10.92 seconds in the quarter mile. The factors are approximations and vary by car. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How long is a quarter mile?
A quarter mile is 1,320 feet, or 402 metres, the most common drag racing distance according to Wikipedia. The eighth mile is 660 feet. Trap speed is measured over the last 66 feet, about 20 metres, before the finish line. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
What is trap speed?
Trap speed is the average speed over the last 66 feet (20 m) before the finish line. Wikipedia describes it as indicating the average speed of the vehicle in that distance. It is closely linked to power, so it is a good check on horsepower. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
Can I estimate horsepower from my ET?
Yes. Rearranged, power = weight x (constant / ET)3. A 3,200 lb car running 11.65 seconds is about 400 hp by Hale. Use power-needed mode with your ET, and remember launch and traction affect ET. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
Does weight or power matter more?
Only the ratio matters in these formulas: ET depends on the cube root of weight over power. Cutting 10 percent of the weight has the same effect as adding about 11 percent more power. The weight to horsepower ratio calculator shows the ratio. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
Does the calculator account for gearing, tires or altitude?
No. It uses power and weight only. Density altitude, tire choice, gear ratios, traction and driver skill all change the real result. Enter the power you expect at the track, and expect real times to vary by a few tenths. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
Can I use kilograms?
Yes. Choose kilograms for the weight and the calculator converts to pounds. A 1,400 kg car is 3,086 lb, and at 300 hp the Hale formula gives 12.67 seconds. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
How do I use this quarter mile calculator?
Choose predict ET or power needed. For prediction, pick a formula, enter horsepower and weight, and read the ET, trap speed and eighth mile figures. For power needed, enter a target ET and the weight, and read the horsepower. Enter your own power and weight, with the driver, in the calculator, and treat the result as an estimate rather than a promise.
References
- [1] Omni Calculator. “Quarter mile calculator.” Omni Calculator. Accessed 2026-10-06.
- [2] CalcHorsepower. “Quarter mile calculator (ET and MPH).” CalcHorsepower. Accessed 2026-10-06.
- [3] Wikipedia contributors. “Drag racing.” Wikipedia. Accessed 2026-10-06.
- [4] Wikipedia contributors. “Horsepower.” Wikipedia. Accessed 2026-10-06.
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