Circularity (○)
Circularity (○), also called roundness, is a form tolerance: each circular cross-section of the feature has to lie between two concentric circles the tolerance apart. It takes no datum.
Easily confused with
How to read it
The circularity symbol is a plain circle in the first compartment of a feature control frame. The zone is set in each cross-section separately: two concentric circles whose radial distance apart equals the tolerance, in Cogorno’s course guide and in the National Physical Laboratory’s guide, which names the control “circularity (roundness)”. Berez’s UNC Charlotte notes, written to ASME Y14.5-2018, call it roundness, define it as the deviation of a 2D cross-section from a perfect circle, and list it among the form controls, with no datum.
Also searched as: ○, circularity gd&t, circularity symbol, roundness symbol.
This explains what a symbol specifies on a drawing. It isn't inspection or design guidance; the drawing and the edition of the standard it cites take precedence.
Look-alikes
Several GD&T symbols are built on a circle. Cylindricity ⌭ sets the circle between two slanted lines and covers the whole surface of a cylinder at once, where circularity takes one cross-section at a time. The Concentricity (◎) symbol ◎ is two concentric circles, and Position (⌖) ⌖ is a circle with a cross through it. A circle with a capital letter inside, such as Ⓜ, is a modifier that follows the tolerance (maximum material condition), not a characteristic.
Read next
- Next in GD&T symbolsCylindricity (⌭)Cylindricity (⌭) is a form tolerance for a cylinder: every point of its surface has to lie between two coaxial cylinders the tolerance apart. It takes no datum.
- The same shape in P&ID symbolsButterfly valveA butterfly valve, which turns a disk inside the pipe to start, stop or regulate flow. It is drawn as a slanted stroke between two short uprights across the line.
More GD&T symbols
The same shape elsewhere
Browse symbols drawn with circles.
Sources
- Fundamental Good Practice in the Design and Interpretation of Engineering Drawings for Measurement Processes, Measurement Good Practice Guide No. 79, David Flack and Keith Bevan, 2005, National Physical Laboratory (UK), Chapter 4, Form tolerances
- Fundamentals of Geometric Dimensioning and Tolerancing (GD&T), Part I, Jaime Berez, seminar adapted from an undergraduate mechanical engineering course, version 2.1.0, 2023, Center for Precision Metrology, University of North Carolina at Charlotte (Zenodo), Slides 27 and 31
- Geometric Dimensioning and Tolerancing for Mechanical Design: Instructors’ Guide, Gene R. Cogorno, guide to the McGraw-Hill textbook, rev. 10/12/2020, Technical Training Consultants, Chapter 5, Form, review answers
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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