How do I use this calculator?
This calculator allows you to convert between 1/4 mile time and 1/8 mile time using a conversion factor.
Calculator Operations:
- Enter the 1/4 mile time and the conversion factor to calculate the 1/8 mile time.
- Enter the 1/8 mile time and the conversion factor to calculate the 1/4 mile time.
The default conversion factor is set to 1.57, which is commonly used for this calculation. You can adjust this value if needed.
Use the calculate button when all known values have been entered and use the reset button to clear the values from the calculator.
Convert 1/4 mile elapsed time to 1/8 mile ET or 1/8 mile time to 1/4 mile ET using a 1.57 drag racing factor, with results in seconds.
Calculator Functions
The calculator estimates a drag-racing elapsed time at one distance from a time at the other. Results also show the answer with factors of 1.55 and 1.58. Select a function to open it in the calculator.
| Function | Use it when | You enter |
|---|---|---|
| 1/4 mile ET to 1/8 mile ET | You have a quarter-mile time | 1/4 mile ET in seconds |
| 1/8 mile ET to 1/4 mile ET | You raced an eighth-mile track and want a quarter-mile estimate | 1/8 mile ET in seconds |
Both functions have an optional conversion factor from 1.3 to 1.8. If you leave it alone, the calculator uses 1.57.
1/4 Mile to 1/8 Mile Time Formulas
| T1/8 | 1/8 mile ET, over 660 feet (seconds) [1] |
| T1/4 | 1/4 mile ET, over 1,320 feet (seconds) [1] |
| F | Conversion factor, 1.57 by default. Typical drag-racing ratios run about 1.55 to 1.58 |
The reverse function is T1/4 = T1/8 × F, so an 8.00 second eighth-mile estimates to 12.56 seconds.
This table uses F = 1.57, rounded to three decimals.
| 1/4 mile ET (s) | 1/8 mile ET (s) |
|---|---|
| 7 | 4.459 |
| 8 | 5.096 |
| 9 | 5.732 |
| 10 | 6.369 |
| 11 | 7.006 |
| 12 | 7.643 |
| 12.5 | 7.962 |
| 13 | 8.280 |
| 13.5 | 8.599 |
| 14 | 8.917 |
| 14.5 | 9.236 |
| 15 | 9.554 |
| 15.5 | 9.873 |
| 16 | 10.191 |
| 17 | 10.828 |
| 18 | 11.465 |
| 19 | 12.102 |
| 20 | 12.739 |
| 22 | 14.013 |
| 24 | 15.287 |
Why the factor is near 1.57
At constant power, time grows with distance to the 2/3 power [2], so doubling the distance multiplies the time by about 1.587. The calculator’s default of 1.57 sits just below that.
Limits of This Estimate
- The factor is an empirical rule of thumb, and the real ratio depends on the car, launch and track. These estimates are based on the best available data and estimations.
- The results show the answer at factors of 1.55 and 1.58 to give a sense of the spread. A 12.5 second quarter-mile gives 7.962 seconds at 1.57, 8.065 at 1.55 and 7.911 at 1.58.
Sources
- NIST, Guide to the SI (SP 811), Appendix B.8: mile and foot definitions
- Lin, The Inverse Velocity Force and Automotive Physics, Am. J. Phys., 2026: general physics of motion at constant power
