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  • The two primary factors to determine the permissible unbalance (also called the balancing tolerance) are the weight of the rotating part (mass) and the highest operational speed.

  • Based on experimental data, the potential for damage due to unbalance can be expressed as "Balancing Quality Grade", or G.

  • The EasyBalance instrumentation system has a built-in ISO balancing quality calculator. Just enter rotor weight, service speed and desired ISO quality (G number), and click CALCULATE


Balance quality grades are standardized in ISO 1940.

Balance quality grade

Vibration velocity in
mm per second

Rotor types
General examples

G 100 100 Crankshaft drives of large Diesel engines
Complete engines for trucks and locomotives
G 40 40 Crankshaft drives for engines of trucks and locomotives
G 16 16 Parts of crushing machinery
Parts of agricultural machinery
G 6.3 6.3 Fly-wheels
Aircraft gas turbine rotors
Electrical armatures
Process plant machinery
Pump impellers
G 2.5 2.5 Machine-tool drives
Turbo compressors
Small electric armatures
Turbine-driven pumps
G 1 1 Grinding machine drives
Textile bobbins
Automotive turbochargers
G 0.4 0.4 Gyroscopes
Spindles for high-precision applications

The smaller the number, the smoother the operation