What is Hale's formula for quarter-mile ET?

Hale's formula is ET = 6.290 × (W/HP)^(1/3), where W is the vehicle's weight in pounds and HP is the wheel horsepower at the tires. It is empirically derived from thousands of drag-strip runs and is accurate to ±0.3 seconds for traction-limited, well-driven cars on a prepped track.

How do I back-calculate horsepower from a quarter-mile time slip?

Rearrange Hale's formula: HP = W × (6.290 / ET)³. Enter your measured ET and vehicle weight, and the calculator solves for implied wheel horsepower.

What is the difference between elapsed time and trap speed?

ET is the total time from launch to the finish. Trap speed is measured over the last 66 feet. A high trap speed with a slow ET indicates a poor launch or traction issues.

How does the 1/8-mile ET relate to the 1/4-mile ET?

ET₁/₈ ≈ ET₁/₄ × 0.625. For bracket racers, ET₁/₄ ≈ ET₁/₈ × 1.60.

Quarter-Mile ET Calculator

Predict elapsed time and trap speed from weight and power, or back-calculate wheel HP from a time slip.

Vehicle Weight(at strip, with driver)

Wheel Horsepower(at tires, not flywheel)

whp

Predicted Quarter-Mile ET

12.96 sec

@ 113.6 mph trap speed

1/8-Mile ET

8.10 sec

Power-to-Weight

114.3 whp/1klb

Formula: ET = 6.290 × (W/HP)^(1/3) — Hale's empirical equation. Assumes good traction and a competent launch. Traction loss adds 0.2–0.6 sec.

What This Calculator Does

The quarter-mile elapsed time (ET) calculator predicts drag-strip performance from vehicle weight and wheel horsepower using Hale's empirical formula — the same base equation used by drag racers worldwide. It also estimates 1/8-mile ET, calculates trap speed, and works in reverse: enter a time slip ET to back-calculate the implied wheel horsepower. Compare your result against the production-car reference table below.

It combines Calculation Mode, Vehicle Weight, Wheel Horsepower, Measured ET (for HP back-calc) to estimate Predicted Quarter-Mile ET, Trap Speed, 1/8-Mile ET.

Formula & Method

Hale's quarter-mile formula:

ET_{1/4} = 6.290 \times \left(\frac{W}{HP}\right)^{1/3}

where

W

is vehicle weight in lb and

HP

is wheel horsepower. Trap speed:

v_{trap} = 234 \times \left(\frac{HP}{W}\right)^{1/3}\,\text{mph}

1/8-mile ET approximation:

ET_{1/8} \approx ET_{1/4} \times 0.625

Back-calculate HP from measured ET:

HP = W \times \left(\frac{6.290}{ET}\right)^{3}

Notation used in the formulas: $R$ = Predicted Quarter-Mile ET; $x_{1}$ = Calculation Mode; $x_{2}$ = Vehicle Weight; $x_{3}$ = Wheel Horsepower; $x_{4}$ = Measured ET (for HP back-calc).

Method summary: inputs are normalized to consistent units, core equations are evaluated, then secondary values are derived and rounded for display.

Use this calculator for quick scenario analysis. Start with baseline values, change one driver at a time, and compare how sensitive the results are to each input shown above.

Worked Examples

Street car — 3,500 lb, 400 whp

ET = 6.290 × (3500/400)^(1/3) = 6.290 × (8.75)^(1/3) = 6.290 × 2.062 = 12.97 seconds Trap speed = 234 × (400/3500)^(1/3) = 234 × 0.485 = 113.5 mph 1/8-mile ET ≈ 12.97 × 0.625 = 8.11 seconds Sanity check: A 3,500 lb car with 400 whp putting down a [email protected] is realistic for a modified muscle car on street tires with a competent driver.

Back-calculate HP from time slip — 11.50 seconds at 3,200 lb

HP = 3200 × (6.290 / 11.50)^3 = 3200 × (0.5470)^3 = 3200 × 0.1637 = 524 whp (implied) If the dyno shows 450 whp but the car ran 11.50, you likely have better traction or a lower real-world weight than assumed. Conversely, if the car ran slower, check for traction loss or drivetrain efficiency loss (typical: 15–18% from flywheel to wheels for RWD automatics).

Production-Car Quarter-Mile Reference Table

Factory stock, best published ET. Actual times vary by conditions, driver, and tires. Sources: Car and Driver, Motor Trend, Road and Track long-term tests.

Vehicle	Weight (lb)	Flywheel HP	ET (sec)	Trap (mph)
Dodge Viper ACR (2017)	3,374	645	10.9	128
Chevy Corvette Z06 (2023)	3,647	670	10.6	132
Ford Mustang Shelby GT500 (2020)	4,225	760	10.6	131
Dodge Challenger Demon 170 (2023)	4,575	1,025	8.91	151
Tesla Model S Plaid (2021)	4,766	1,020	9.23	152
Porsche 911 Turbo S (992)	3,582	640	9.9	136
BMW M3 Competition (G80)	3,810	503	11.1	122
Chevy Camaro ZL1 (2022)	4,120	650	11.0	131
Ford Mustang GT (5.0, 2024)	3,827	486	11.8	117
Dodge Charger Scat Pack (2022)	4,165	485	11.7	118
Honda Civic Type R (FL5)	3,117	315	12.6	113
Subaru WRX STI (2021)	3,417	310	12.7	109
Toyota Supra A90 (2023)	3,380	382	11.7	116
Ford Mustang Mach-E GT Performance	4,950	480	11.8	116
Chevrolet Corvette Stingray (C8)	3,366	490	11.2	122
Dodge Charger Hellcat (2021)	4,586	717	10.9	133
Ford F-150 Raptor R (2023)	5,697	700	12.2	114

Common Mistakes

Using flywheel horsepower instead of wheel horsepower — drivetrain loss is typically 12–20%. A 500 flywheel-hp car might put down only 410–440 whp at the tires.
Ignoring traction — Hale's formula assumes perfect traction. A car spinning the tires will run slower than predicted. Drag radials, prepped track surface, and launch technique add 0.2–0.6 seconds to the model.
Not accounting for altitude — air density drops ~3% per 1,000 ft. A car that runs 11.5 at sea level might run 12.0 at 5,000 ft altitude. Add roughly 1% ET per 1,000 ft elevation.
Using curb weight vs race weight — fuel, driver, and passengers add 150–200 lb. Always use the actual weight at the strip, ideally weighed in.
Confusing 1/4-mile and 1/8-mile ETs — many local tracks run 1/8-mile (660 ft). Multiplying 1/8-mile ET by 1.60 gives a rough 1/4-mile estimate (more accurate than × 2).

Frequently Asked Questions

What is Hale's formula for quarter-mile ET?: Hale's formula is ET = 6.290 × (W/HP)^(1/3), where W is the vehicle's weight in pounds and HP is the wheel horsepower at the tires. It is empirically derived from thousands of drag-strip runs and is accurate to ±0.3 seconds for traction-limited, well-driven cars on a prepped track.
How do I back-calculate horsepower from a quarter-mile time slip?: Rearrange Hale's formula: HP = W × (6.290 / ET)³. Enter your measured ET and vehicle weight, and the calculator solves for implied wheel horsepower.
What is the difference between elapsed time and trap speed?: ET is the total time from launch to the finish. Trap speed is measured over the last 66 feet. A high trap speed with a slow ET indicates a poor launch or traction issues.
How does the 1/8-mile ET relate to the 1/4-mile ET?: ET₁/₈ ≈ ET₁/₄ × 0.625. For bracket racers, ET₁/₄ ≈ ET₁/₈ × 1.60.

Recommended Tools

Some links below are affiliate links. As an Amazon Associate, MCPCalc earns from qualifying purchases, at no extra cost to you. Learn more.

dragy DRG70-C GPS Performance Meter - Measure your real 1/4-mile ET and trap speed to within 0.01s.
How to Make Your Car Handle - Fred Puhn's classic guide to suspension and chassis tuning.

Inputs Used

Calculation Mode: Used directly in the calculation.
Vehicle Weight: Total vehicle weight at the strip — curb weight + fuel + driver. Use actual scale weight if available.
Wheel Horsepower: Power at the drive wheels — not flywheel HP. Typical drivetrain loss: 15% for RWD MT, 18% for RWD AT.
Measured ET (for HP back-calc): Time slip ET from the drag strip. Only used in back-calculate mode.

Related Calculators

0-60 Time Calculator - Estimate 0-60 mph time from vehicle weight and wheel horsepower.
0–100 km/h Calculator - Estimate 0–100 km/h time from vehicle kerb weight (kg) and power (kW or hp). Includes European and JDM production-car reference table and metric–imperial conversion.
Compression Ratio Calculator - Calculate engine static and dynamic compression ratio from bore, stroke, chamber volume, head gasket, deck height, and piston dome or dish. Includes octane recommendation, forced-induction effective CR, and altitude/boost correction.
Horsepower Calculator - Convert torque and RPM to horsepower.
Fuel Economy Calculator - Calculate MPG and L/100km from fuel used and distance traveled.
Fuel Cost Calculator - Estimate trip fuel cost from distance, efficiency, and fuel price.
EV Range Calculator - Estimate EV range from battery capacity and efficiency.
EV Charging Calculator - Estimate charging time from battery size, start/end SOC, and charger power.