Wheat Penny Different Size Than Memorial

I don't believe that's correct. All Lincoln cents, both wheats and memorials, have measured 19.05 mm in diameter, which is exactly 3/4 of an inch. I think Indian Head cents are also the same.

If your naked eye can detect differences a little as 5 hundredths of a millimeter (about the width of a human hair), you are likely the Bionic Man. And, you'd make one heck of a coin grader.

A delta as small as that could be caused by any number of steps in the manufacturing process and is probably negligible (0.26% difference) or at least within tolerances.

I'm willing to bet it is just a rounding error. I'm sure when the small cent was first specced by the mint it was done as 3/4", the U.S. not being metrically inclined in those days. When various authorities / authors / reference sources converted to metric the overly picky or unthinking ones converted as 19.05 mm, where as those with a better understanding of the relevance of significant digits just converted it as 19 mm.
This same thing bugs me when I see instructions on doing something that will say "cut a piece about 6 inches long (152.4 mm). If they are telling you to estimate about 6 inches and then cut, why the h would you say OR 152.4 mm? Lets just call it 150 mm to stay with the spirit of the thing.

Agree the 19 mm figure was an "error"; perhaps it was a matter of convenience for the writer to round down.

I edited the Wiki article but haven't found decent online sources to reference.

Thanks All!