NTS Not to scale
Not to scale · Anotaciones de plano · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Dimension 45 NTS (underlined) on enlarged detail” states a not to scale requirement.
What controls
Warning that a particular dimension or detail is not drawn in proportion to the rest of the drawing: what is shown is larger or smaller than the scale would indicate. It usually appears as an underline beneath the affected dimension, and it typically originates from a later change to the value without redrawing the geometry, or from a detail exaggerated for clarity. The stated dimension remains fully valid and mandatory: what cannot be trusted is the drawing.
How to verify
The part is inspected against the numerical value of the dimension, which is what governs, using the instrument appropriate to its tolerance. The note itself only affects how the drawing is read. When in doubt, the valid reference is the 3D model of the part, if one exists and the drawing designates it as the master geometry, never the geometry drawn in that area.
Common mistakes when interpreting it
- Scaling dimensions off the drawing in an area marked as not to scale.
- Reading the note as meaning the dimension is approximate: the dimension is exact, it is the drawing that is not.
- Overlooking that a not-to-scale dimension usually signals a recent change, and working to an old revision.
How to get it in the workshop / if it comes out of tolerance
Treat it as a red flag: where there is a not-to-scale dimension there has usually been a change, so make sure you are working to the latest drawing revision. Never derive dimensions in that area by measuring on the paper or the PDF, and never use it to estimate geometry that is not dimensioned. If you need a dimension that is missing and falls in that area, ask for it instead of scaling it.
If the machined part does not match what is drawn, check for not-to-scale dimensions before assuming a calculation error. If what you measure on the drawing contradicts the dimension, the dimension governs. And if the affected area has undimensioned geometry you need for programming, do not derive it from the drawing: ask.
Related symbols
Other symbols in Plan annotations
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