Rotor Balancing Tolerance Calculator (ISO 1940-1 / VDI 2060)
Calculate the permissible residual unbalance for a rotor from its balance quality grade (G), service speed and mass — the tolerance a balancing machine must hit. Based on the ISO 1940-1 standard relation, with the grade reference table below.
How it is calculated
ISO 1940-1 defines the permissible specific residual unbalance as e_per = 1000·G / ω, where ω = 2πn/60 is the angular velocity at service speed n (rpm) and G is the balance quality grade (mm/s). Numerically e_per is in g·mm/kg (equivalent to µm of mass-centre eccentricity).
Multiplying by rotor mass gives the total permissible residual unbalance U_per = e_per · m (g·mm). For a two-plane rotor the tool splits it evenly across the correction planes — a common first approximation; ISO 1940-2 gives the exact plane-by-plane allocation for asymmetric rotors.
These are standard tolerances for planning. Confirm against the rotor drawing and your balancing machine’s minimum achievable residual unbalance (U_mar).
Balance quality grades (ISO 1940-1)
| Grade | Typical application |
|---|---|
| G 0.4 | Precision grinder spindles, gyroscopes |
| G 1 | Grinding-machine drives, small electric armatures, audio/video drives |
| G 2.5 | Gas & steam turbines, machine-tool drives, medium/large armatures, pumps |
| G 6.3 | Fans, flywheels, pump impellers, general machinery & machine-tool parts |
| G 16 | Drive/propeller shafts, crushing & agricultural machinery, engine parts |
| G 40 | Car wheels & rims, drive shafts |
| G 100 | Complete reciprocating engines for cars/trucks |
| G 250 | Crankshaft drives of large, fast diesel engines |
Frequently asked questions
What balance quality grade do I need?
It depends on the machine type. Fans, flywheels and pump impellers are typically G6.3; machine-tool drives and turbines G2.5; precision spindles G1 or finer. Use the reference table above and confirm against the equipment specification.
Why does higher speed need tighter balancing?
Permissible eccentricity is inversely proportional to speed (e_per ∝ 1/n). Doubling the service speed halves the allowable residual unbalance for the same grade, because centrifugal force rises with speed.
What is g·mm/kg?
It is specific unbalance — residual unbalance per unit rotor mass — and is numerically equal to the mass-centre eccentricity in micrometres (µm). Multiply by rotor mass to get the total permissible unbalance in g·mm.
Need balancing machines or rotor sourcing?
ASEAN Machine sources dynamic balancing machines and precision rotating equipment from vetted China manufacturers, with delivery and support across Thailand and ASEAN. Tell us your rotor spec and we will help you specify the right machine.