Each turbine wheel and compressor wheel model generally have the same turbine diameter (highest diameter), but different steps (lowest diameter). Each type of step (trim), has different blowing characteristics.

- TRIM values are expressed as 45, 50, 55, etc… and can only go from 0 to 100. A value of 100 means Dp is equal to Dg.
- A large TRIM indicates a large turbine diameter.
- A TRIM of 55, gives 10% more caudal than a TRIM of 50.
- TRIM is used in the same way for turbine wheels as for compressor wheels.
- TRIM is calculated through the following formula:
TRIM = ( Dp / Dg )² x 100
Example: If Dg = 50 mm and Dp = 35 mm
TRIM = ( 35/50 )² x 100 = 49