A one-page GD&T quick reference: every geometric characteristic symbol grouped by type, whether it needs a datum, which material condition modifiers it accepts, and the formulas used to check position, bonus tolerance and virtual condition. Each symbol links to its full page.
ASME Y14.5; size limits also control form unless stated otherwise
How to use this cheat sheet
Find the symbol in the left column, then read across: whether it needs a datum and which modifiers it accepts. If a drawing shows a modifier this sheet says the symbol cannot take, ask the designer before you inspect.
For a position callout with Ⓜ, compute the bonus from the measured size first, then compare the measured position diameter with the stated tolerance plus bonus.
Concentricity and symmetry were removed in ASME Y14.5-2018. They are listed because older drawings still use them; check which edition the drawing invokes.
Example: Position with bonus tolerance
Given
Hole size limit Ø10.0–10.4 mm, so the MMC size is Ø10.0
Feature control frame: position, Ø0.2 Ⓜ, datums A | B | C
Measured: hole Ø10.25 mm; centre offset from true position Δx = 0.12 mm, Δy = 0.09 mm
Find
The measured position deviation
The allowed position tolerance at this size
Whether the hole is acceptable for position
Solution
Position deviation as a diameter zone.Ø_actual = 2·√(0.12² + 0.09²) = 2 × 0.15 = Ø0.30 mm
The hole departs from MMC by its size difference, which becomes bonus tolerance.bonus = 10.25 − 10.00 = 0.25 mm
Allowed tolerance at the measured size.Ø0.20 + 0.25 = Ø0.45 mm
Compare.Ø0.30 ≤ Ø0.45 → accept
Answer: The hole is Ø0.30 from true position against an allowed Ø0.45 at its size, so it passes position (size must also be within Ø10.0–10.4, which it is).
Printable cheat sheet
The PDF is one US Letter page that also prints on A4 without cropping. The 2:3 PNG is the same sheet as an image, sized for a phone lock screen or a pin. Both are made from the formulas in the tables above, so they always match.
ASME Y14.5-2018 has 12 geometric characteristic symbols; the 2009 edition had 14, including concentricity and symmetry, which this sheet keeps for older drawings. Modifiers such as Ⓜ, Ⓛ and Ⓟ are separate.
Which symbols never use a datum?
The form controls: straightness, flatness, circularity and cylindricity. They control a feature’s shape on its own, so a datum would have nothing to relate to.
Is this sheet a substitute for the standard?
No. It summarizes common rules in plain language. The governing standard is whichever edition of ASME Y14.5 or ISO 1101 the drawing invokes.
