What does NTS mean on a drawing?

Not to scale. The view is drawn for clarity, not size, so you cannot measure it. Use the written dimensions and notes.

What does "do not scale" mean on a drawing?

Build only to the written dimensions. If a size you need is missing, ask whoever issued the drawing instead of measuring it.

What happens to the scale when a drawing is printed smaller?

The scale changes with it. A 1/4" = 1'-0" plan printed at half size is really at 1/8" = 1'-0", and a 1:50 plan printed at half size is really at 1:100. The scale note on the sheet does not change, so it is now wrong.

Why do drawings have a graphic scale bar?

A scale bar is printed as part of the drawing, so it shrinks or grows with the copy. Measuring against the bar still works on a resized print, when the written scale note does not.

Scale reading: lesson 5 of 6

Written dimensions, NTS and reduced prints

Decide which length to use. Get 10 right to finish. Pick feet and inches or metric in the box below.

Your architect's scale reads 23'-4" for this wall. What length do you build?

The rule: written dimensions win

When a drawing gives a dimension, build to that number. Paper stretches, copies shrink, PDFs get printed with "fit to page" turned on. A scaled length is a check, not an instruction. If the number and your scale disagree by a lot, tell whoever issued the drawing.

Your scale reads 12'-0". Build it 12'-4".

NTS: not to scale

A view marked NTS is drawn to show how something goes together, not how big it is. The scale of the other views on the sheet does not apply to it. Use the written dimensions only. A single dimension can also be marked as not to scale, often by underlining it.

Reduced and enlarged prints

Plans are often printed at half size to save paper. A half-size print of a 1/4" = 1'-0" plan is at 1/8" = 1'-0", and a half-size 1:50 plan is at 1:100. The scale note on the sheet is not updated, so measuring with it gives half the real length.

At half size this sheet is really 1/8" = 1'-0". 1 1/2 in is 12'-0", not 6'-0".

If the sheet has a graphic scale bar, measure against it instead. The bar is part of the drawing, so it shrank by the same amount and still reads true.

Common mistakes

Scaling a PDF on screen. Zoom changes everything you see.
Measuring an NTS detail with the scale of the plan next to it.
Using the scale note on a print you did not print yourself.

Questions

What does NTS mean on a drawing?: Not to scale. The view is drawn for clarity, not size, so you cannot measure it. Use the written dimensions and notes.
What does "do not scale" mean on a drawing?: Build only to the written dimensions. If a size you need is missing, ask whoever issued the drawing instead of measuring it.
What happens to the scale when a drawing is printed smaller?: The scale changes with it. A 1/4" = 1'-0" plan printed at half size is really at 1/8" = 1'-0", and a 1:50 plan printed at half size is really at 1:100. The scale note on the sheet does not change, so it is now wrong.
Why do drawings have a graphic scale bar?: A scale bar is printed as part of the drawing, so it shrinks or grows with the copy. Measuring against the bar still works on a resized print, when the written scale note does not.

Explained in our own words and checked against trade school textbooks. Metric scales follow the ISO 5455 series.