Industrial Fans, Blowers & Air Movement Equipment worked example

Impeller Balance Tolerance with allowable residual unbalance of 63 g-mm: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop allowable residual unbalance to 63 g-mm, then walk the calculation through step by step. Calculate balance tolerance margin by comparing allowable residual unbalance with measured or required residual unbalance.

The inputs for this scenario

  • Allowable residual unbalance: 63 g-mm (the input this scenario stresses; the baseline uses 125)
  • Measured residual unbalance: 92 g-mm (held at the documented default)
  • Reference balance tolerance: 125 g-mm (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Impeller balance tolerance margin = allowable residual unbalance - measured residual unbalance.
  • Balance margin percent works out to -23.2 % at these inputs, and this is the headline figure for the scenario.
  • Impeller balance tolerance margin works out to -29 g-mm at these inputs.
  • Allowable residual unbalance works out to 63 value at these inputs.
  • Measured residual unbalance works out to 92 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where allowable residual unbalance sits at 125 g-mm and the headline result is 26.4 %, this scenario comes in 188% below the baseline at -23.2 %.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to allowable residual unbalance, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It compares single residual-unbalance values and does not perform the ISO grade calculation itself (which depends on rotor mass and service speed), nor does it distinguish single-plane from two-plane balancing.

Results at a glance

  • Balance margin percent: -23.2 % (headline result)
  • Impeller balance tolerance margin: -29 g-mm
  • Allowable residual unbalance: 63 value
  • Measured residual unbalance: 92 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Impeller Balance Tolerance calculator, set allowable residual unbalance to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.