GD&T symbols, shown as tolerance zones
A geometric tolerance is a zone the feature has to stay inside. Each page below draws that zone in 3D and lets you deform the part until it falls outside.
Written to ISO 1101, the standard behind European drawings, with the ASME Y14.5 difference noted wherever the two disagree.
The parts of the notation itself — the frame the tolerance lives in, the references it is measured from, and the material condition modifiers that change what it demands.
- No datumFeature control frameThe box the whole tolerance lives in, read left to right, one cell at a time.Open symbol
- No datumDatumThe reference a tolerance is measured from, and the order that decides how the part is held.Open symbol
- No datumMaximum material conditionThe modifier that hands back tolerance as the feature moves away from its worst case.Open symbol
How true a feature is to its own ideal shape. Form tolerances stand alone: they are measured on the feature itself, so they carry no datum reference.
- No datumStraightnessHow straight a single line on a surface, or a derived axis, has to run.Open symbol
- No datumFlatnessHow far a whole surface may depart from a perfect plane.Open symbol
- No datumCircularityHow round a single cross-section has to be, taken one slice at a time.Open symbol
- No datumCylindricityRoundness, straightness and taper of a whole cylindrical surface, in one control.Open symbol
How a feature sits at an angle relative to a datum — parallel, square, or at a stated theoretically exact angle. Orientation controls form as a by-product.
- Datum requiredParallelismHow closely a surface or axis has to run parallel to a datum.Open symbol
- Datum requiredPerpendicularityHow square a surface or axis has to sit relative to a datum.Open symbol
- Datum requiredAngularityHow closely a surface or axis has to hold a stated angle to a datum.Open symbol
Where a feature sits relative to datums and to theoretically exact dimensions. Location controls orientation and form as a by-product.
- Datum requiredPositionWhere a feature has to sit, measured from theoretically exact dimensions and datums.Open symbol
- Datum requiredConcentricityWhether the derived median line of a feature is coaxial with a datum axis.Open symbol
- Datum requiredSymmetryWhether a feature sits evenly either side of a datum median plane.Open symbol
What a rotating feature does relative to a datum axis. Runout combines form and location into one measurement taken as the part turns.
A zone that follows the true shape of a surface, offset either side of it. Profile can control form alone, or form together with orientation and location once a datum is named.
Available calculators
We read the drawing before we talk about price. These calculators are that same language, out in the open.
Engineering calculatorsThese pages explain the published standards for reference and describe the tolerance zones they define. The values shown in the examples are illustrative. What a given part can hold depends on its geometry, material and process, and is agreed per drawing.