Approximate roundness error from the maximum and minimum radii measured around a circumference (minimum zone method) for shafts and precision rotating parts.
圆度 = 最大半径 − 最小半径（最小区域法近似）。
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Roundness deviation (minimum zone) | Roundness is the minimum radial separation of two concentric circles enclosing the profile | ISO 12181-1:2011, Geometrical product specifications (GPS) - Roundness - Part 1 |
| Least-squares reference circle | A least-squares reference circle is a common alternative evaluation | ISO 12181-2:2011, Geometrical product specifications (GPS) - Roundness - Part 2 |
| Tolerance zone | The roundness tolerance zone is the area between two concentric circles in one cross-section | ISO 1101:2017, Geometrical product specifications (GPS) - Geometrical tolerancing |
| Versus cylindricity | Roundness concerns a single cross-section and does not control axial form | ISO 1101:2017, Geometrical product specifications (GPS) - Geometrical tolerancing |