Definition
A dimensional tolerance is the permitted variation on a single dimension, such as a length, diameter or angle, typically expressed as a plus/minus value or limit dimensions. It governs size, whereas a geometric tolerance (GD&T) governs form, orientation, location or runout independently of size.
Why dimensional tolerance alone isn't always enough
A tight dimensional tolerance without a corresponding geometric tolerance can still leave form or orientation loosely controlled, which is one reason GD&T exists: to control what a plus/minus dimension alone cannot.
Where it appears on the drawing
Directly on the dimension itself, either as an explicit plus/minus value, as limit dimensions, or implied by a general tolerance block (such as ISO 2768) when no explicit tolerance is given.
Common mistakes
Assuming a tight dimensional tolerance also controls form or orientation; a diameter within tolerance can still be out-of-round or tilted unless a geometric tolerance also constrains it.
A tight dimensional tolerance without a corresponding geometric tolerance can still leave form or orientation loosely controlled, which is one reason GD&T exists: to control what a plus/minus dimension alone cannot.
See how Blake reviews a partFrequently asked questions
Is dimensional tolerance the same as GD&T?
No, dimensional tolerance controls size; GD&T (geometric tolerance) controls form, orientation, location or runout, and the two are often used together.
What happens if no tolerance is given on a dimension?
It usually falls back to a general tolerance block, such as ISO 2768, referenced elsewhere on the drawing.
Can a part be within its dimensional tolerance but still fail?
Yes, if a geometric requirement (flatness, position, perpendicularity) is not separately met.