---
type: "gdt-symbol"
name: "Circularity"
symbol: "○"
unicode: "U+25CB"
category: "form"
category_name: "Form controls"
datum_required: "never"
tolerance_zone: "Two concentric circles in each cross-section"
aliases: ["circularity gdt", "roundness", "out of round"]
standard: "ASME Y14.5 (cited, not reproduced); ISO 1101"
verified: "August 1, 2026"
url: https://shopmath.org/gdt/circularity
---

# Circularity (○) — GD&T Symbol, Tolerance Zone and Datum Rules

Checked one cross-section at a time: every point around the section must lie in the ring between two concentric circles whose radii differ by the tolerance value. Each section is judged independently, so circularity catches lobing and out-of-round but not taper or bend along the length.

- **Symbol**: ○ (Unicode U+25CB)
- **Category**: Form controls
- **Tolerance zone**: Two concentric circles in each cross-section
- **Datum reference**: never references a datum
- **Standard**: ASME Y14.5 (cited, not reproduced); ISO 1101

## Circularity at a Glance

| Property | Value |
| --- | --- |
| Characteristic | Circularity |
| Symbol | ○ |
| Unicode codepoint | U+25CB |
| Category | Form controls |
| Tolerance zone | Two concentric circles in each cross-section |
| Datum reference | never references a datum |
| Standard | ASME Y14.5 (cited, not reproduced); ISO 1101 |

## How Circularity Behaves

Circularity belongs to the form controls group. Control the shape of a single feature against itself. Never reference a datum.

## Other Form controls Controls

The controls in the same category — the ones a drawing is choosing between when it specifies circularity.

| Control | Symbol | Tolerance zone or effect | Datum |
| --- | --- | --- | --- |
| [Straightness](https://shopmath.org/gdt/straightness.md) | ⏤ | Two parallel lines (surface element) or a cylinder (axis) | never references a datum |
| [Flatness](https://shopmath.org/gdt/flatness.md) | ⏥ | Two parallel planes | never references a datum |
| [Cylindricity](https://shopmath.org/gdt/cylindricity.md) | ⌭ | Two coaxial cylinders | never references a datum |

## Sources and Method for Circularity

### Circularity definition

- **Source**: Symbols and codepoints: Unicode Character Database (Unicode License v3). Characteristic list cross-checked against NASA MSFC GD&T Basics (public domain). Descriptions written from scratch; no ASME Y14.5 text reproduced.
- **Method**: compiled
- **Verified against**: Unicode Character Database codepoint check; 98/98 structural checks passed

### Assumptions

- Descriptions are original prose. No ASME Y14.5 definitional text, worked example or figure is reproduced — the standard is cited, not copied.
- Symbol glyphs and codepoints are from the Unicode Character Database; a drawing may render the same characteristic with a different font.
- Dataset scope: EXCLUDED: all ASME Y14.5 definitional text, worked examples and figures. Every description on this site is original prose.

**Data last verified**: August 1, 2026

## Common Questions About Circularity in GD&T

### What does Circularity mean in GD&T?

Checked one cross-section at a time: every point around the section must lie in the ring between two concentric circles whose radii differ by the tolerance value. Each section is judged independently, so circularity catches lobing and out-of-round but not taper or bend along the length.

### What is the GD&T symbol for circularity?

Circularity uses the ○ symbol — Unicode U+25CB. It sits in the first compartment of the feature control frame.

### Does Circularity need a datum?

Circularity never references a datum. The tolerance zone floats to best-fit the feature, so there is nothing to reference it to.

### What is the tolerance zone for Circularity in GD&T?

The circularity tolerance zone is: Two concentric circles in each cross-section.

## Related pages

- Previous control: [Flatness](https://shopmath.org/gdt/flatness.md) (⏥)
- Next control: [Cylindricity](https://shopmath.org/gdt/cylindricity.md) (⌭)
- All symbols: [GD&T symbol reference](https://shopmath.org/gdt.md)
- Tolerances: [ISO 286 fit reference](https://shopmath.org/fits.md)

---

*Source: [ShopMath](https://shopmath.org/gdt/circularity) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*