Litres consumed per 100 kilometres; lower is better. Standard metric efficiency unit.

Energy lost deforming tires as they roll. Low-pressure or wide tires raise it.

Automotive Calculators

Quarter-Mile ET Calculator

2026-09-27 6 min

Quarter-mile elapsed time from race weight and wheel horsepower — ET = 5.825 × (W/HP)⅓.

Elapsed Time: 12.55 s
Average Speed: 71.7 mph; Over the 1,320 ft

Calculator

Race Weight(lb)

Wheel Horsepower(whp)

whp

Results update live as you type

Live statistics

Elapsed Time

12.55 s

Average Speed

71.7 mph

Over the 1,320 ft

Results

Optimal

Elapsed Time

12.55s

Average Speed

71.7mph

Over the 1,320 ft

Planning estimate from standard automotive formulas. Validate with dyno, timeslip or datalog data when precision matters.

Visualizations

Results overview

12.6Elapsed Time

71.7Average Speed

Elapsed Time vs. Race Weight

Elapsed Time

12.6s

820

Formula

Hale ET relation isolated — launch-averaged acceleration over the standing quarter.

ET = 5.825 × (W ÷ HP)⅓

Variables

Symbol	Name	Unit	Description
W	Race weight	lb	With driver and fuel
HP	Wheel power	whp	Effective average

Explanation

ET rewards traction and gearing as much as power — the first 60 feet dominate the clock.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Record the inputs.

Race Weight:3500 lb

Wheel Horsepower:350 whp

Result: 2 inputs ready

Step 2

Apply the formula.

ET = 5.825 × (W ÷ HP)⅓

Result: Primary result = 12.55 s

Step 3

Read every derived output.

Elapsed Time:12.55 s

Average Speed:71.7 mph

Result: Elapsed Time = 12.55 s

Final Answer

12.55

Worked Examples

See how the calculator works with different scenarios.

Scenario

3,400 lb, 380 whp.

Inputs

Weight:3,400 lb

Power:380 whp

Calculation

ET = 5.825 × (8.95)⅓ = 12.08

Result

12.08 s ET.

Interpretation

Drag-radial, good-air number for a heads/cam car.

Understanding Your Result

Your Result: Elapsed Time: 12.55 s

What This Means

Time from green to stripe.

Why It Matters

ET wins bracket races — consistency and launch beat peak power.

Professional Interpretation

Treat the primary result as a planning estimate, then validate on a dyno, at the track, or with logged sensor data. If measured numbers disagree by more than ~10%, re-check inputs (units are the usual culprit) before changing parts.

Recommendations

•Double-check units on every input before trusting the result
•Compare against the worked example below to sanity-check magnitude
•Validate with measured data (dyno, timeslip, datalog) when it matters

Learn — fuel economy, deeply

Elapsed time is the launch’s report card, weighted by the whole run.

1 · Where the gallon goes (energy path)

Engine heat

60–70% lost

Coolant + exhaust carry most energy away. Hybrids recover some via Atkinson cycle + regen.

Driveline

5–15% lost

Transmission, differential, accessories. CVTs and 8–10 speed autos lose less.

Aero drag

∝ v²

Doubles from 55→78 mph. Roof boxes hurt more than trunks.

Rolling + brakes

10–20%

Tires, weight, stops. Regen braking (hybrid/EV) reclaims city braking energy.

4 · Measure like a pro (the 3-tank protocol)

Fill to first click at the same pump, record the odometer (Tank 0).
Drive normally for 2–3 tanks; always refill to first click at the same pump.
MPG = total miles ÷ total gallons across all tanks — averaging kills pump-click noise.
Cross-check with the trip computer; a persistent >10% gap means the computer needs calibration — or the car needs service.
Log with an OBD-II dongle for per-trip MPG if you want to isolate commute vs. highway behavior.

Practical Tips

•Start from the default values — they describe a typical combination
•Use the sensitivity chart to see which input moves the result most
•Keep units consistent (all inches or all mm, never mixed)

Common Mistakes

Mixing units (inches with mm, psi with kPa)

Convert every input to the unit shown on its field before calculating.

Trusting a single output blindly

Cross-check with the worked example and, when it matters, a dyno or datalog.

Assumptions

This calculator makes the following assumptions to provide estimates:

Steady-state model: Formulas assume stabilized conditions; transients, heat soak and traction limits are excluded.

Standard factors: Empirical constants (BSFC, VE, drivetrain loss) use typical values — your combination may differ.

Limitations

Be aware of these limitations when using this calculator:

Estimate, not measurement: Predictions carry real-world scatter of roughly ±5–15% depending on the model.

No transient effects: Shift time, wheelspin, spool lag and heat soak are not modeled here.

Frequently Asked Questions

Answers to common questions about this calculator.

Why is my ET slower than predicted?

Usually traction (60-ft time), heat soak, altitude or shifting — check 60-ft first.

Does weight reduction help ET?

Yes — 100 lb is worth roughly 0.1 s and 1 mph of trap.

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Related Guides

Deepen your understanding with these educational resources.

Automotive Guides

Build planning, measurement protocol and validation how-tos

Glossary

Technical terms used in mortgage calculations explained in plain language.

MPG: Miles per gallon. Distance travelled per gallon of fuel; higher is better. US gallon = 3.785 L.
L/100 km: Litres consumed per 100 kilometres; lower is better. Standard metric efficiency unit.
MPGe: Miles per gallon-equivalent. EV metric: miles travelled on 33.7 kWh (energy of 1 gal of gasoline).
CAFE: Corporate Average Fuel Economy — US fleet-average efficiency standard enforced by NHTSA.
Rolling resistance: Energy lost deforming tires as they roll. Low-pressure or wide tires raise it.
Aerodynamic drag: Air resistance growing with the square of speed — why highway MPG falls fast above 60 mph.
Hypermiling: Driving techniques (coasting, steady speed, anticipation) that maximise real-world MPG.
OBD-II: On-board diagnostics port. Scanners and dongles read live MPG, fuel trim and fault codes.

Authoritative References

Trusted sources and standards referenced by this calculator.

EPA — FuelEconomy.gov DOE — Fuel-Efficient Driving Tips NHTSA — Driving Safety & Efficiency SAE International — Fuel Economy Standards Consumer Reports — MPG Truth IRS — Standard Mileage Rates

Applicable Standards

EPA Fuel Economy Testing (40 CFR Part 600)CAFE — Corporate Average Fuel Economy Standards (NHTSA)WLTP — Worldwide Harmonised Light Vehicle Test ProcedureSAE J1321 / J1711 — Fuel consumption test proceduresISO 2575 — Road vehicles symbols & efficiency markings

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Page Information

Last Updated:

2026-09-27

Version:

2.0.0

References:

License:

Free to use for educational and professional purposes.