How many GD&T symbols are there?

14 geometric characteristics — the controls that go in the first compartment of a feature control frame — plus 8 modifiers and material-condition symbols that qualify them, 22 in all.

Which GD&T symbols require a datum?

8 of the geometric characteristics always reference a datum: Angularity, Perpendicularity, Parallelism, Position, Concentricity, Symmetry, Circular Runout, Total Runout. 4 never do — the form controls, which judge a feature against itself. Profile controls can go either way.

What is the true position symbol in GD&T?

⌖ (Unicode U+2316). The workhorse of the system. Basic dimensions from the datum reference frame fix an exact ideal location, and the tolerance defines a zone around it that the feature's axis or centre plane must stay within. Because a round zone is a diameter rather than a square envelope, position gives about 57 percent more usable area than an equivalent coordinate tolerance.

What is the difference between ASME Y14.5 and ISO 1101?

They are two standards for the same job and they differ in detail — the default relationship between size and form, how the envelope requirement is invoked, and which modifiers exist. A drawing names the standard it is drawn to, and that standard governs how every symbol on it is interpreted.

Reference · GD&T

GD&T Symbols — All 14 Geometric Characteristics and Modifiers

https://shopmath.org/gdt · data verified August 1, 2026

GD&T has 14 geometric characteristic symbols and 8 modifiers. 8 of the characteristics always reference a datum and 4 never do — that split is the fastest way to read a feature control frame. Each symbol page gives the tolerance zone it defines, its datum rule and its Unicode codepoint.

Characteristics: 14
Modifiers: 8
Categories: 4
Verified: August 1, 2026

The Fourteen GD&T Geometric Characteristic Symbols

The controls that go in the first compartment of a feature control frame, in standard order: form, profile, orientation, location, runout.

GD&T geometric characteristic symbols, tolerance zones and datum rules
Symbol	Category	Datum	Tolerance zone	Unicode
Straightness	Form	never	Two parallel lines (surface element) or a cylinder (axis)	U+23E4
Flatness	Form	never	Two parallel planes	U+23E5
Circularity	Form	never	Two concentric circles in each cross-section	U+25CB
Cylindricity	Form	never	Two coaxial cylinders	U+232D
Profile of a Line	Profile	optional	Two curves offset from the true profile, in each cross-section	U+2312
Profile of a Surface	Profile	optional	Two surfaces offset from the true profile	U+2313
Angularity	Orientation	always	Two parallel planes (or a cylinder, for an axis) at the basic angle	U+2220
Perpendicularity	Orientation	always	Two parallel planes (or a cylinder, for an axis) normal to the datum	U+27C2
Parallelism	Orientation	always	Two parallel planes (or a cylinder, for an axis) parallel to the datum	U+2225
Position	Location	always	A cylinder (or two parallel planes) centred on the true position	U+2316
Concentricity	Location	always	A cylinder centred on the datum axis, applied to derived median points	U+25CE
Symmetry	Location	always	Two parallel planes centred on the datum centre plane	U+232F
Circular Runout	Runout	always	Full indicator movement in each single cross-section	U+2197
Total Runout	Runout	always	Full indicator movement across the whole surface	U+2330

A form control never references a datum; an orientation, location or runout control always does; profile controls may be applied either way. Every row links to that control's own page.

GD&T Modifiers and Material Condition Symbols

Symbols that change how a tolerance is interpreted or verified rather than defining a control of their own.

GD&T modifiers and material condition symbols
Symbol	Category	Datum	Tolerance zone	Unicode
Maximum Material Condition (MMC)	Modifier	never	n/a — modifier	U+24C2
Least Material Condition (LMC)	Modifier	never	n/a — modifier	U+24C1
Regardless of Feature Size (RFS)	Modifier	never	n/a — modifier	U+24C8
Projected Tolerance Zone	Modifier	never	Zone projected above the feature	U+24C5
Free State	Modifier	never	n/a — modifier	U+24BB
Tangent Plane	Modifier	never	n/a — modifier	U+24C9
Unequally Disposed Profile	Modifier	never	Profile band split unevenly about the true profile	U+24CA
Diameter	Modifier	never	n/a — modifier	U+2300

Modifiers appear after the tolerance value or after a datum reference, and they change what the stated tolerance actually permits — a bonus tolerance under MMC, for instance, is real material the inspection has to allow for.

GD&T Symbol Categories and What Each Group Controls

GD&T symbol categories
Category	Symbols	Controls	What the group does
Form controls	4	Straightness Flatness Circularity Cylindricity	Control the shape of a single feature against itself. Never reference a datum.
Orientation controls	3	Angularity Perpendicularity Parallelism	Control the angle of a feature relative to a datum, but not its distance.
Location controls	3	Position Concentricity Symmetry	Control where a feature sits relative to a datum reference frame.
Modifiers and material conditions	8	Maximum Material Condition (MMC)Least Material Condition (LMC)Regardless of Feature Size (RFS)Projected Tolerance Zone Free State Tangent Plane Unequally Disposed Profile Diameter	Change how a geometric tolerance is interpreted or verified.

A category appears here only when it carries at least three symbols; the profile and runout pairs are listed in the tables above.

Common Questions About GD&T Symbols

How many GD&T symbols are there?: 14 geometric characteristics — the controls that go in the first compartment of a feature control frame — plus 8 modifiers and material-condition symbols that qualify them, 22 in all.
Which GD&T symbols require a datum?: 8 of the geometric characteristics always reference a datum: Angularity, Perpendicularity, Parallelism, Position, Concentricity, Symmetry, Circular Runout, Total Runout. 4 never do — the form controls, which judge a feature against itself. Profile controls can go either way.
What is the true position symbol in GD&T?: ⌖ (Unicode U+2316). The workhorse of the system. Basic dimensions from the datum reference frame fix an exact ideal location, and the tolerance defines a zone around it that the feature's axis or centre plane must stay within. Because a round zone is a diameter rather than a square envelope, position gives about 57 percent more usable area than an equivalent coordinate tolerance.
What is the difference between ASME Y14.5 and ISO 1101?: They are two standards for the same job and they differ in detail — the default relationship between size and form, how the envelope requirement is invoked, and which modifiers exist. A drawing names the standard it is drawn to, and that standard governs how every symbol on it is interpreted.

Sources and Method for the GD&T Symbol Reference

GD&T geometric characteristics and modifierscompiled

Unicode Character Database (Unicode License v3); characteristic list cross-checked against NASA MSFC GD&T Basics (public domain); descriptions written from scratch

Verified against gdt: 98 checks passed across 1 harness(es)

Compiled from independent public sources that agree cell-for-cell.

Assumptions

The standards are cited, never reproduced: no ASME Y14.5 definitional text, worked example or figure appears on this site. Every description here is original prose written against the public-domain characteristic list.
ASME Y14.5 and ISO 1101 differ in detail. Where a drawing names a standard, that standard governs the interpretation of every symbol on it.
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

How this data is built and checked →

How to Cite This GD&T Symbol Reference

Citation

ShopMath. "GD&T Symbols — All 14 Geometric Characteristics and Modifiers." ShopMath, verified August 1, 2026, https://shopmath.org/gdt

BibTeX

@misc{shopmath-gdt,
  title        = {GD&T Symbols — All 14 Geometric Characteristics and Modifiers},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/gdt}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/gdt