Is it “Diameter of the Circles” or “Diameters of the Circles”?

Question

If there are multiple circles and they all have the exact same diameter, should it be expressed as "the diameter of the circles" or "the diameters of the circles"?

First I thought it would be "diameters" because each of these circles individually has one diameter even if the lengths are the same, but then I thought if the diameters are all the same, they could probably be referred to as "the diameter". And I'm thinking, if the circles each have a different diameter, it should be "the diameters of the circles". Is this correct? I want to know the correct way of use.

Answer 1

@nnnnnn is correct:

You may refer to the single (same) diameter that the various circles share in either the singular or in the plural and still be grammatically correct.

The only concern comes into play with the fact that without explicitly calling out the fact that the many circles share a single value for their various diameters, using the singular may be seen as an error (or at least sloppy writing) if the audience is either academic or pedantic.

Answer 2

It depends on your intended meaning. If I say:

The diameters of the circles are all less than the diameter of the derived shape.

I am talking about diameter as a measurement, and I imply that there could be a variety of different measurements. If there is one measurement for all the circles, I would use the singular.

What is the diameter of the circles in that design?

I might be one of those "pedantic" folks Omnidisciplinarianist referred to in their answer though. A lot of people don't make the same small distinctions in meaning that I do.