Eighth-mile times to quarter-mile projections
1/8 to 1/4 Mile Conversion Chart
Ran an eighth-mile pass and wondering what that means over a full quarter? Use the chart below or type your numbers into the converter to project your quarter-mile time and trap speed.
- Multiplier (time)
- 1.560 ×
- Multiplier (speed)
- 1.25 ×
The conversion rule
The standard rule of thumb is: 1/4-mile ET ≈ 1/8-mile ET × 1.56 and 1/4-mile MPH ≈ 1/8-mile MPH × 1.25. The factors are shared in drag-racing circles and referenced in the Stealth316’s horsepower / ET / MPH calculator notes. They work best for a well-balanced car with consistent traction.
Conversion chart: 1/8 mile to 1/4 mile ET
| 1/8 mile ET (s) | ≈ 1/4 mile ET (s) |
|---|---|
| 5.00 | 7.80 |
| 5.25 | 8.19 |
| 5.50 | 8.58 |
| 5.75 | 8.97 |
| 6.00 | 9.36 |
| 6.25 | 9.75 |
| 6.50 | 10.14 |
| 6.75 | 10.53 |
| 7.00 | 10.92 |
| 7.25 | 11.31 |
| 7.50 | 11.70 |
| 7.75 | 12.09 |
| 8.00 | 12.48 |
| 8.25 | 12.87 |
| 8.50 | 13.26 |
| 8.75 | 13.65 |
| 9.00 | 14.04 |
| 9.25 | 14.43 |
| 9.50 | 14.82 |
| 9.75 | 15.21 |
| 10.00 | 15.60 |
Conversion chart: 1/8 mile to 1/4 mile speed
| 1/8 mile MPH | ≈ 1/4 mile MPH |
|---|---|
| 70 | 87.5 |
| 75 | 93.8 |
| 80 | 100.0 |
| 85 | 106.3 |
| 90 | 112.5 |
| 95 | 118.8 |
| 100 | 125.0 |
| 105 | 131.3 |
| 110 | 137.5 |
| 115 | 143.8 |
| 120 | 150.0 |
Going the other way, multiply a quarter-mile ET by 0.641 and a quarter-mile speed by 0.8.
When the conversion misleads
The projection assumes the car keeps accelerating at the same relative rate. Cars that spin up in the first half, run out of gear or change aero will not match the chart. Boosted cars often hold their pace better than the rule suggests. Treat it as a planning number and confirm at a full-length track.
Frequently asked questions
How do I convert 1/8 mile ET to 1/4 mile ET?
Multiply the eighth-mile elapsed time by 1.56. For example, 7.00 s becomes about 10.92 s.
How do I convert 1/8 mile MPH to 1/4 mile MPH?
Multiply by 1.25. A 90 mph eighth-mile speed projects to about 112.5 mph in the quarter.
Why 1.56?
It is an empirical ratio, near the figure you get from constant acceleration physics. Because acceleration falls at speed, it is a rule of thumb rather than a law.
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