GD&T Reference→Form→Circularity

○

CIRCULARITY

FORM

Controls how round a cross-section is

✓ NO DATUM NEEDEDASME Y14.5-2018 §12.4

Circularity (also called roundness) controls how much any circular cross-section of a feature can deviate from a perfect circle. The tolerance zone is an annular region between two concentric circles. It applies to each cross-section independently — not the full length of the feature.

WHEN TO USE IT

Use circularity on shafts, bores, or spherical features where the roundness of individual cross-sections matters for function — such as hydraulic seals, bearings, or rotating components. It does not control how the cross-sections align with each other along the length of the feature.

COMMON MISTAKES

✕

Confusing circularity with cylindricity — circularity controls one cross-section at a time, cylindricity controls the full surface

✕

Adding a datum reference — circularity is a form control and never uses datums

✕

Applying circularity to flat or non-circular features

✕

Using a circularity tolerance larger than the size tolerance — it must be smaller

IS YOUR CALLOUT CORRECT?

Check these before releasing your drawing.

Is the FCF free of any datum reference letters?

Circularity is a pure form control. No datum should appear in the FCF.

Is the feature actually circular or cylindrical in cross-section?

Circularity only applies to features with circular cross-sections.

Is the circularity tolerance smaller than the size tolerance?

Per Rule #1, the circularity tolerance cannot exceed the total size tolerance.

RELATED SYMBOLS

OTHER FORM CONTROLS

⏥Flatness ⏤Straightness ⌭Cylindricity

Redprint checks circularity automatically

Redprint flags circularity FCFs with datum references and checks that the tolerance value does not conflict with the feature size tolerance.

Try it free — no account needed ← Back to reference