---
type: "gdt-symbol"
name: "Flatness"
symbol: "⏥"
unicode: "U+23E5"
unicode_name: "FLATNESS"
category: "form"
category_name: "Form controls"
datum_required: "never"
tolerance_zone: "Two parallel planes"
aliases: ["flatness gdt", "flatness symbol", "flatness tolerance"]
standard: "ASME Y14.5 (cited, not reproduced); ISO 1101"
verified: "August 1, 2026"
url: https://shopmath.org/gdt/flatness
---

# Flatness (⏥) — GD&T Symbol, Tolerance Zone and Datum Rules

Requires every point of a surface to fall between two parallel planes separated by the tolerance value. Because the zone floats to best-fit the surface, flatness says nothing about where the surface sits relative to anything else — that is what parallelism and profile are for.

- **Symbol**: ⏥ (Unicode U+23E5)
- **Category**: Form controls
- **Tolerance zone**: Two parallel planes
- **Datum reference**: never references a datum
- **Standard**: ASME Y14.5 (cited, not reproduced); ISO 1101

## Flatness at a Glance

| Property | Value |
| --- | --- |
| Characteristic | Flatness |
| Symbol | ⏥ |
| Unicode codepoint | U+23E5 |
| Unicode name | FLATNESS |
| Category | Form controls |
| Tolerance zone | Two parallel planes |
| Datum reference | never references a datum |
| Standard | ASME Y14.5 (cited, not reproduced); ISO 1101 |

## How Flatness Behaves

Flatness 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 flatness.

| 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 |
| [Circularity](https://shopmath.org/gdt/circularity.md) | ○ | Two concentric circles in each cross-section | never references a datum |
| [Cylindricity](https://shopmath.org/gdt/cylindricity.md) | ⌭ | Two coaxial cylinders | never references a datum |

## Sources and Method for Flatness

### Flatness 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 Flatness in GD&T

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

Requires every point of a surface to fall between two parallel planes separated by the tolerance value. Because the zone floats to best-fit the surface, flatness says nothing about where the surface sits relative to anything else — that is what parallelism and profile are for.

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

Flatness uses the ⏥ symbol — Unicode U+23E5 (FLATNESS). It sits in the first compartment of the feature control frame.

### Does Flatness need a datum?

Flatness 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 Flatness in GD&T?

The flatness tolerance zone is: Two parallel planes.

## Related pages

- Previous control: [Straightness](https://shopmath.org/gdt/straightness.md) (⏤)
- Next control: [Circularity](https://shopmath.org/gdt/circularity.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/flatness) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*