Definition
A general tolerance is a table of standard deviations that applies to all dimensions with no tolerance of their own. The table is usually tied to a standard, for example ISO 2768, with a class such as fine, medium or coarse. The allowed deviation grows with the size of the dimension. Standards such as ISO 2768 are periodically revised: always confirm the exact edition and part cited on the drawing itself rather than assuming a fixed, unchanging table.
What it means for the calculation
The chosen class changes the cost of the whole part, not of one dimension. A fine class on a drawing with many dimensions that carry no tolerance of their own forces tighter work, more measuring, and sometimes a finishing pass on faces nobody considered critical. A coarse class leaves room to work faster. So read the class before pricing the individual tolerances: it is often the most expensive line on the drawing that nobody points at.
Where it appears on the drawing
In or beside the title block, as a reference to the standard followed by the class, sometimes with the table itself printed next to it.
Common mistakes
Skipping the general tolerance and pricing only the dimensions that carry their own. Also assuming the class from the same customer's previous drawing still applies: it can differ per drawing and change with a revision.
The chosen class changes the cost of the whole part, not of one dimension. A fine class on a drawing with many dimensions that carry no tolerance of their own forces tighter work, more measuring, and sometimes a finishing pass on faces nobody considered critical. A coarse class leaves room to work faster. So read the class before pricing the individual tolerances: it is often the most expensive line on the drawing that nobody points at.
See how Blake reviews a partFrequently asked questions
Does the general tolerance also cover boxed dimensions?
No, a basic dimension falls outside it; that one has its own feature control frame.
Does ISO 2768 also cover form and location tolerances?
Besides linear and angular dimensions, the standard has a part for general form and location tolerances; which part applies is stated in the reference on the drawing.
What if no general tolerance is given at all?
Then the requirement is incomplete, and asking the customer is cheaper than assuming.