I can’t get the diameter command to work when using the circle command. I select the circle command, specify the center and then type my dimensions, however SketchUp ignores the D command. For example, draw a circle that is .75" I tried all the following, but always got a circle with the radius of 0.75 instead:

There’s a ‘trick’ in v2015 [PC at least - untried on MAC]…
Type the diameter / 2 and it halves the entered value to be the radius.
So the make a circle with a 500 diameter type 500/2 [+Enter] and the radius is taken as 250 - half of the diameter…

It doesn’t work entering unit suffixes, so 500mm/2 will fail.
Also decimal number will fail - 500.5/2 gives a radius of 500.5 NOT 250.25

So it’s only useful for whole numbers
I suspect it’s something to do with how SketchUp interprets ‘fractional’ inch values which never contain these…
With a little more effort it could be properly implemented within SketchUp !

I’m still looking for a truly smart input box that can evaluate, translate, or convert anything you can throw at it–sort of like the Google search box. Regrettably, the apparently unintended ability to divide by two, sometimes, doesn’t exactly rise to the level of “smart.”