Custom Page Sizes

And one other possibility is it doesn't really matter what the dialog assumes is tghe default unit. Most places you can enter dimensions will accept any unit you like as long as you tell ID the unit you want to use after the dimension, such as 5.7 in or 3p6, or 927 pt, and ID will do the math and convert to whatever happens to be showing for units in the dialog.

If it's in the page setup dialog boxes, that is a system setting for your Mac.

Go to System Preferences, open Language & Region panel, click "Advanced", then set "Measurement units" to US/UK instead of Metric...

Open InDesign preferences, without any documents open, and select from the Units and Increments tab the units you want, such as Inches. When you next set up a new document the units should be the one you selected in preferences.

Yes.

Open InDesign. Do not open a document.

Go to your Apple menu (Mac) or your Edit menu (PC) and select the Preferences menu command. Go to Units and Increments option in the list to the left of the Preferences dialog box, and in the Ruler Units section select the Inches option for the Horizontal: and Vertical: options boxes. Click the OK button, then shut down the program.

After doing that, InDesign should show you measurements in inches forevermore ... or at least until you change those settings again.

This should get you the results you want.

Randy