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Balance grade calculator: permissible unbalance per ISO 21940-11

Permissible residual unbalance of a rotor from grade G, mass and speed (ISO 21940-11, formerly ISO 1940-1), and the correction mass. Free, no sign-up.

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Pre-filled example

A 100 kg fan rotor, grade G 6.3, running at 3,000 rpm, corrected in two planes at a 150 mm radius.

mm/s
kg
rpm
mm

Result

2,005g·mmPermissible residual unbalance

Permissible eccentricity
20.05µm
Unbalance per plane
1,003g·mm
Correction mass at the radius
13.37 g
  • Caution : Half per plane: symmetric rotor, bearings equally distant from the centre of gravity (ISO 21940-11).
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Balancing tolerance attached to the repair work order

Here, the calculator is free and the result is gone when you close the page. In Reglova, it is attached to the work order on the right machine: you find it again at the next breakdown, and on audit day.

The CMMS software comparison, our gaps included
  • Attached to the work order with its inputs: the server recalculates it, it stays verifiable.
  • On the technician's phone, even without a network.
  • In the machine's history, for the next breakdown.
  • The asset's nameplate data pre-fills the calculation.
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Reglova · Calculations · Work order WO-AT01-04219
Silent video, 33 s: from the work order for an oil leak on a shear cylinder, the tightening torque of an M12 bolt, then "Attach to the work order". A step to tighten it to 93.1 N·m lands in the checklist (step text from the French demo data). Watch the video

When to calculate a permissible unbalance

  1. 01

    Give the balancing shop or contractor a tolerance in figures.

  2. 02

    Check a balancing report after a fan repair.

  3. 03

    Estimate the balancing weight to weld or bolt onto the impeller.

Good to know

Splitting the unbalance equally between two planes assumes a symmetrical rotor with bearings equidistant from the centre of gravity. Common grades: G 6.3 for fans, pumps and motors, G 2.5 for machine tools.

Balance grade G formula and correction planes

The balance quality grade G sets the product of the permissible eccentricity of the centre of gravity and the angular velocity. From it, the calculator derives the rotor's permissible residual unbalance in g·mm, the eccentricity in µm, the share of each correction plane and the corresponding mass at the correction radius.

Formula · Reference documents

ω = 2π·n/60 ; e = 1,000·G/ω (µm) ; U = e·m (g·mm) ; per plane U/2 ; mass = U/r

ISO 21940-11 (G 6.3 fans, pumps, motors ; G 2.5 machine tools ; G 16 drive shafts)

Inputs and accepted ranges
InputUnitAccepted rangeExample
Balance quality grade Gmm/s0.1 to 4,0006.3 mm/s
Rotor masskg0.001 to 1,000,000100 kg
Service speedrpm1 to 200,0003,000 rpm
Correction planes1 to 22
Correction radiusmm1 to 10,000150 mm
Calculated results
  • Permissible residual unbalanceg·mm
  • Permissible eccentricityµm
  • Unbalance per planeg·mm
  • Correction mass at the radiusg
What the calculator flags
  • Half per plane: symmetric rotor, bearings equally distant from the centre of gravity (ISO 21940-11).

Fan and rotor repairs traced from report to restart

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  • Work orders on the phone, even without a network
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