How do I label every circle with its diameter in AutoCAD automatically?

What cadssistant does

1. Selects the circles on the layer and reads their centres and radii.
2. Creates a TEXT entity per circle, all in one step: Ø plus the diameter to one decimal, placed beside the circle (the snippet puts it just outside the right edge), height 2.5 unless you give a number.
3. Replies with the count and the height and layer it used. "Make them dimensions instead" swaps the texts for DIMDIAMETER dimensions, one command each.

The same task in AutoLISP

(progn
  (setq ss (ssget "_X" '((0 . "CIRCLE") (8 . "HOLES"))) i 0 n 0)
  (if ss
    (repeat (sslength ss)
      (setq ed (entget (ssname ss i)) i (1+ i)
            c (cdr (assoc 10 ed)) r (cdr (assoc 40 ed)))
      (entmake (list '(0 . "TEXT")
                     (cons 10 (polar c 0.0 (* 1.2 r)))
                     (cons 40 2.5)
                     (cons 1 (strcat "%%c" (rtos (* 2 r) 2 1)))))
      (setq n (1+ n))))
  n)

Text height 2.5, placed at 1.2 × radius to the right of each centre. %%c is the diameter symbol in TEXT.

Good to know

• %%c renders as Ø in TEXT; MTEXT uses \U+2205 instead. cadssistant picks the one that matches the entity it creates.
• A 1.2 × radius offset lands inside a crowded pattern. Say "with leaders" and it places each label clear of the holes with an MLEADER.

More in draw and lay out

• How do I fill a closed shape with a grid of circles in AutoCAD?
• How do I array a selected object in a grid in AutoCAD by typing what I want?
• How do I hatch a selected area with a pattern in AutoCAD from a sentence?
• How do I draw holes on a bolt circle (PCD) in AutoCAD?