Estimate quarter-mile time and trap speed from horsepower and race weight, or work back to the horsepower or weight needed for a given 1/4 mile time.

Car plus driver, fuel and equipment.

Optional settings
The models use different power conventions. A basis conversion requires your assumed drivetrain loss.

Horsepower Quarter Mile Formula

Choose a solve mode. The Huntington coefficient pair is K = 6.290 and C = 224, using peak engine power delivered at the clutch. The Hot Rod Calc implementation uses K = 5.825 and C = 234 with estimated rear-wheel power.

T = K×(W/HP)(1/3)
HP = W×(K/T)3
W = (T/K)3 × HP
  • T = quarter-mile time in seconds
  • W = vehicle weight in pounds
  • HP = horsepower in the selected model’s power convention
  • K = 6.290 for Huntington or 5.825 for Hot Rod Calc. Trap speed in mph = C*(HP/W)(1/3), with C = 224 or 234 respectively

The calculator converts entries to pounds, mechanical horsepower and seconds. It uses the chosen solve mode and model. When the entered/requested power basis differs from the model, wheel power = engine power × (1 − assumed loss/100).

  • If time is missing, it estimates quarter-mile time from weight and horsepower.
  • If horsepower is missing, it estimates horsepower from weight and quarter-mile time.
  • If weight is missing, it estimates vehicle weight from horsepower and quarter-mile time.

Quarter-Mile Time Reference

These are informal descriptions, not performance classifications or safety limits. They do not calibrate either model.

Quarter-mile time General performance range Typical description
15 seconds or slower Normal street vehicle Average acceleration
13 to 14.9 seconds Quick street vehicle Noticeably faster than average
11 to 12.9 seconds Fast performance vehicle Strong acceleration
10 seconds or quicker Very fast drag performance Often requires serious setup and traction

Unit Conversions Used

Input unit Base unit conversion
1 kilogram 2.20462 pounds
1 kilowatt 1.34102 horsepower
1 minute 60 seconds

Example

Example 1: Find quarter-mile time

Using the Huntington model, enter a race weight of 3,200 lb and engine/clutch power of 400 hp.

T = 6.290×(3200/400)(1/3) = 12.58 seconds

The estimated quarter-mile time is 12.58 seconds, with a model trap speed of 112 mph. These are empirical predictions, not guaranteed track results.

FAQ

Should you use curb weight or race weight?

Use the weight of the vehicle as it will run the quarter mile. This usually means race weight, including the driver, fuel, and any cargo or equipment in the car.

Is the horsepower result wheel horsepower or engine horsepower?

The selected model determines its power convention: Huntington uses peak clutch power, while the Hot Rod Calc implementation uses estimated rear-wheel power. Select the entered or requested basis. A different basis requires an explicit drivetrain-loss assumption; this conversion is not a measured loss.

Why is the quarter-mile result only an estimate?

The formula is based on weight and horsepower only. Real quarter-mile times also depend on traction, gearing, shift speed, aerodynamics, tire choice, weather, and driver skill.