Free quarter mile (ET) calculator
Enter your vehicle's weight and horsepower to estimate its drag-strip 1/4-mile elapsed time (ET) and trap speed from power-to-weight — updated live, as you type.
On this page15 sections
Estimates only, from power-to-weight. Real times depend on traction, launch and weather.
Results are estimates. Consult a professional.
How the quarter-mile calculator works
A drag race is a contest of power against weight. This quarter-mile calculator takes two numbers — your vehicle's weight and its horsepower — and estimates two results: the elapsed time (ET) it would take to cover a standing 1/4 mile, and the trap speed it would be travelling at the finish line. Both come from the same idea, the power-to-weight ratio, which is simply how much power each pound of car has to move.
The math is empirical, not theoretical. In the 1950s, engineer Roger Huntington timed hundreds of cars down the strip, plotted their power-to-weight against their results, and fit a curve to the data. The constants in the formulas below are that line of best fit. They assume good traction and a competent launch, which is why a calculator can only ever hand you an estimate — the strip decides the rest.
The quarter-mile ET and trap speed formulas
Two equations do the work. The first turns power-to-weight into an elapsed time; the second turns it into a trap speed. Weight is in pounds and power is in horsepower, and both formulas take a cube root — that cube root is why the relationship is not linear.
The 6.290 and 224 constants are the common Huntington/Fox pair. Roger Huntington's original 1950s fit used a slightly quicker ET constant, ET = 5.825 × (weight ÷ power)^(1/3), which this calculator also reports so you can see the spread between the two well-known curves.
These are standard empirical drag-race equations. The Huntington (6.290 / 224), Fox and Hale curve fits are documented by Omni's quarter-mile calculator (https://www.omnicalculator.com/physics/quarter-mile); the 5.825 ET constant is the one Wallace Racing uses to back-calculate horsepower from a timeslip.A worked example: a 3,400 lb car with 300 hp
Maria has a 3,400 lb coupe that dynos at 300 hp and wants a target to chase at her next test-and-tune night. She enters the weight with herself in the seat and the horsepower, and reads off the estimated ET and trap speed.
Step 1 — Find the power-to-weight ratio
Divide weight by power for the ET side: 3,400 ÷ 300 = 11.33. The cube root of 11.33 is 2.246.
Step 2 — Estimate the elapsed time
Multiply by the ET constant: 6.290 × 2.246 = 14.13 seconds. Using Huntington's quicker 5.825 constant instead gives 13.08 seconds — the spread shows why different sites quote slightly different times.
Step 3 — Estimate the trap speed
Flip the ratio for speed: 300 ÷ 3,400 = 0.0882, and its cube root is 0.445. Then 224 × 0.445 = 99.7 mph at the finish line.
Quarter-mile times by power-to-weight
If you just want a ballpark before you plug in your own numbers, this table shows the estimated ET and trap speed for common weight-and-power combinations. These assume good traction and a clean launch — treat them as the best the car can do, not a guarantee.
| Weight × power | Power-to-weight (hp/lb) | Est. ET (s) | Est. trap (mph) |
|---|---|---|---|
| 3,000 lb × 200 hp | 0.067 | 15.51 | 90.8 |
| 3,400 lb × 300 hp | 0.088 | 14.13 | 99.7 |
| 3,200 lb × 400 hp | 0.125 | 12.58 | 112.0 |
| 3,500 lb × 500 hp | 0.143 | 12.03 | 117.1 |
| 2,800 lb × 250 hp | 0.089 | 14.07 | 100.1 |
| 4,000 lb × 350 hp | 0.088 | 14.17 | 99.4 |
ET uses the 6.290 constant; trap speed uses 224. Figures match this page's calculator exactly. Real times vary with traction, launch and weather.
Notice the last three rows: a 2,800 lb / 250 hp car and a 4,000 lb / 350 hp car land within a tenth of each other, because their power-to-weight ratios are nearly identical. The ratio is what matters — not horsepower alone.
ET vs trap speed: what each number tells you
The calculator gives you two outputs because they measure two different things, and the gap between your estimate and your real timeslip is the most useful diagnostic you have.
Trap speed reflects power
Trap speed is how fast you are going as you cross the line. It is set almost entirely by power-to-weight, because over 1,320 feet the engine has time to show what it has regardless of how messy the start was. A higher trap speed means more power reached the road, full stop. That is why racers trust trap speed as a power gauge more than ET.
ET reflects power plus the launch
Elapsed time is the whole story: power, traction, the 60-foot launch and every shift. A car can trap a high speed yet run a disappointing ET if it spun the tires off the line. So if your trap matches the estimate but your ET is slower, the time is hiding in the first 60 feet — a traction or launch problem, not a power problem.
Why your real quarter-mile time is slower than the estimate
Almost everyone runs slower than the calculator at first, and that is expected. The formulas describe a car that hooks cleanly and launches well; the real strip rarely cooperates on the first few passes. These are the variables the math cannot see.
- Traction — the single biggest variable. A car that spins the tires off the line loses tenths the formula never accounts for. A prepped track and stickier tires can drop your ET on identical power.
- The 60-foot launch — your first 60 feet sets the tone for the whole run. A slow 60-foot time on a high trap speed is the classic signature of wheelspin or a soft launch.
- Gearing and shift time — gears that are too tall or too short, or slow manual shifts, leave power on the table the estimate assumes you keep.
- Density altitude — hot, humid or high-elevation air makes less power. The same car runs quicker on a cool, dry night than on a muggy afternoon.
- Aerodynamics — drag matters more the faster you go, so high-trap cars feel it most near the stripe.
Crank vs wheel horsepower: which to enter
The horsepower you type changes the answer, so it matters which figure you use. There are two, and they are not the same.
Crank (advertised) horsepower
Crank horsepower is the number on the brochure, measured at the engine before the drivetrain. Some of it is lost to the transmission, driveshaft and axles before it reaches the pavement — often 10–15% on a typical rear-wheel-drive car. Enter crank horsepower and the calculator will tend to predict a quicker ET than you really run.
Wheel horsepower
Wheel horsepower (whp) is what a chassis dyno reads at the tires, after those losses. It is the more honest input for a quarter-mile estimate, because the timeslip reflects power that reached the road. If you only know crank power, you can convert it on the horsepower calculator, then come back here with the wheel figure for a closer estimate.
How to run a quicker quarter mile
If your real ET trails the estimate, you usually do not need more power — you need a better pass. The fastest gains come from the launch and the setup, not the wallet.
- Fix the 60-foot first. Lower your tire pressure for grip, find the right launch RPM, and feed in the power as the tires take it. The first 60 feet pays back the most.
- Shed weight before you add power. Power-to-weight cuts both ways — pulling 100 lb out of a 3,400 lb car has the same effect on the ratio as a small power gain, for free.
- Run when it's cool and dry. Lower density altitude means more power and grip, so an evening pass usually beats a hot afternoon one.
- Use a real timeslip to check your work. Compare your trap speed to the estimate to confirm the engine is making its power, then compare ET to find where the launch is leaking time.
- Match your gearing. Make sure you cross the line near the power peak in the right gear, so you are not short-shifting or bouncing off the limiter.
Quarter-mile and drag-racing definitions
How accurate is this quarter-mile calculator?
The arithmetic is exact: for any weight and power you enter, the cube-root formulas return the precise ET and trap speed those empirical curves predict. The Huntington/Fox constants used here reproduce the published worked examples to the decimal.
What the formulas cannot promise is the strip. They were fit to well-launched cars with good traction, so for a clean pass they typically land within roughly half a second to a second of a real ET, and closer still on trap speed. Spin the tires, run in hot air, miss a shift or enter crank power instead of wheel power, and the gap widens. Use the estimate as a target and a diagnostic — compare it to your timeslip to learn whether you are leaving time in the engine or in the launch — rather than as a guaranteed number.
Accuracy notes follow the published guidance on these empirical equations: they assume good traction and a competent driver, estimate wheel horsepower from the run, and diverge with poor traction, gearing, weather and aerodynamics.Frequently asked questions about the free quarter mile (ET) calculator
About this Quarter Mile (ET) calculator
This quarter-mile calculator runs entirely in your browser — nothing you enter is sent anywhere. It uses the classic Huntington/Fox empirical drag-racing equations to estimate elapsed time and trap speed from your vehicle's weight and horsepower, and reports Roger Huntington's original ET constant alongside so you can see the spread between the well-known curves.
It's one of the free automotive tools in our transportation calculators collection, part of the wider library at calculator-s.cloud. Estimates assume good traction and a competent launch; real times depend on the strip.