What Does Torque Converter Slip Percentage Tell You?

Torque converter slip percentage tells you how much speed is being lost between the engine and the transmission. In a torque converter, the engine spins the pump side, and the fluid inside drives the turbine side — but they never spin at exactly the same speed. That difference is called slip.
Slip % = (Actual RPM − Theoretical RPM) / Theoretical RPM × 100
The Purpose of the Calculator
To diagnose problems: If the slip percentage stays high while cruising at a steady speed, your locking mechanism has failed (causing heat and wasted gas).

To confirm performance: If the slip percentage is extremely low (under 2%) while accelerating hard, your engine is lugging; if it’s too high (over 10%) while cruising, you are wasting fuel.