How to use this calculator
- Enter measured RPM and speed. Use logged values from the same instant.
- Enter tire diameter. Use rolling tire diameter or revs-per-mile equivalent.
- Enter drivetrain ratios. Set transmission, final drive and transfer ratio.
- Read slip. Review slip RPM and percentage.
How it works
The calculator finds wheel RPM from speed and tire circumference, multiplies by the overall drivetrain ratio, then compares against measured engine RPM: slip % = (measured rpm - locked rpm) / locked rpm x 100.
Use engine RPM for a clean theoretical check, or final drive ratio when changing axle ratio.
Worked example
Verified against the live calculator
If locked mechanical RPM is 2,800 rpm and measured RPM is 3,000 rpm, slip is about 200 rpm, or 7.1%.
Frequently asked questions
How do you calculate torque converter slip?
Calculate the locked mechanical RPM from road speed, tire diameter and gear ratios, then compare it with measured engine RPM.
What does positive slip mean?
Positive slip means measured engine RPM is higher than the locked mechanical RPM at the same road speed.
Why would slip be negative?
Negative slip usually means tire diameter, road speed, gear ratio or measurement data is wrong.
Does this work for manual clutches?
Yes. The same comparison can screen clutch slip when the drivetrain should be mechanically locked.
Method & assumptions
- Requires measured RPM and speed from the same gear and moment in time.
- Converter lockup, load, tire growth and shift transients can change observed slip.