Glossary
What Is GD&T? Definition for Engineers
GD&T is a symbolic system for defining allowable variation in a part's form, orientation, location and profile. It turns functional intent into callouts a supplier can inspect.
Geometric dimensioning and tolerancing (GD&T) is a symbolic system for defining allowable variation in a part's form, orientation, location and profile. ASME identifies Y14.5 as the authoritative guideline for stating and interpreting GD&T on drawings, models and related documents.
What is GD&T? Explained in plain language
GD&T replaces stacked plus/minus limits with symbols that describe how a feature may vary while still working. Example: a bolt hole pattern gets a position tolerance called out from datums instead of a chain of dimensions.
GD&T controls and reference standards
| Control | What it governs | Typical size | Reference |
|---|---|---|---|
| Position | Location of a feature from datums | Design-specific | ASME Y14.5-2018 |
| Flatness | Form of a surface | Design-specific | ASME Y14.5-2018 |
| Profile | Surface or line boundary | Design-specific | ASME Y14.5-2018 |
| Datum reference frame | Degrees of freedom | Feature-specific | ASME Y14.5-2018 |
How GD&T is used in manufacturing
- Drawing-based definition: broadly compatible; interpretation depends on correct standards use.
- Model-based definition: embeds requirements digitally; software and data exchange must be controlled.
- Inspection planning: links controls to gauges or CMM routines; can increase upfront engineering effort.
- Use calibrated equipment.
Related terms
Have a drawing to quote?
Upload it with quantity and material to start a quote.
FAQ
Common questions
Which standard should a drawing use?
Use the standard explicitly stated by the design authority, commonly ASME Y14.5 or an applicable ISO GPS standard. Do not mix ASME Y14.5 and ISO GPS conventions casually on one drawing.
What is the difference between GD&T and plus/minus tolerancing?
GD&T defines geometric relationships and functional variation; plus/minus tolerancing limits individual dimensions.
Ready when you are
Need parts made to a GD&T drawing?
Sourcing Repository collects quotes from a vetted supplier network, manages quality and inspection, and delivers parts. Send your drawing and request a quote.
Your files stay confidential. NDA available on request.