Quarter Mile ET & Horsepower Calculator

Estimate a Quarter-Mile Time (or the Horsepower Behind One) From Weight Alone

You don't need a dyno or a track day to get a solid estimate of quarter-mile performance — weight and horsepower alone get you surprisingly close, using the same empirical formulas drag racers and engine builders have relied on for decades. Go one direction to predict elapsed time and trap speed for a build you're planning, or go backward from a trap speed or ET you already ran to estimate how much power was actually behind it.

How to use it

• Pick what you're solving for: ET and trap speed from weight and horsepower, or horsepower from a known trap speed or ET.
• Enter your vehicle's weight with the driver included — curb weight plus roughly 150–180 lb is a reasonable estimate if you haven't weighed it loaded.
• Enter the known value for your chosen mode and get the rest instantly, along with the power-to-weight ratio (lb per hp), the number that ultimately drives all of these formulas.

Real-world use cases

Predicting how much a planned bolt-on power upgrade should drop your quarter-mile time before spending the money. Backing into a rough horsepower estimate for a car with unknown mods, using nothing but a trap speed from a time slip. Comparing two hypothetical builds' weight-to-power ratios to see which one theoretically has the quicker ET on paper.

Frequently asked questions

How accurate are quarter-mile ET calculators?

They're a solid ballpark, typically within a few tenths of a second for a well-driven, well-hooked-up car, but they only account for weight and power. Tire grip, gearing, launch technique, altitude, and drivetrain losses (front-wheel-drive and AWD lose more power to the wheels than rear-wheel-drive) all shift the real result.

What formula is used to estimate ET from horsepower and weight?

ET (seconds) = 6.290 × (weight ÷ horsepower)^(1/3). It's an empirical formula fit to real drag-strip data rather than a physics derivation, which is exactly why it works well as a quick estimate despite ignoring traction and gearing.

How do you estimate horsepower from trap speed?

Using Hale's formula: horsepower = weight × (trap speed ÷ 234)^3. This is the same method commonly used to back into a rough wheel horsepower number from nothing but a time slip's trap speed and the car's weight.

Should I use crank horsepower or wheel horsepower?

Either works as long as you're consistent about what "horsepower" means in your calculation — wheel horsepower (whp) already accounts for drivetrain loss and will give a more realistic ET, while crank/flywheel horsepower will estimate a slightly quicker time than the car will actually run.

Does this account for all-wheel drive traction advantages?

No — the formula is purely about weight-to-power ratio and doesn't model traction, launch RPM, or drivetrain type. An AWD car with excellent grip will often run quicker than this estimate, while a high-power, traction-limited RWD car may run slower.