Spiny Norman said:

dv said:

About 8.35

Well I got that wrongly.

I copied the shape in Solidworks as best I reasonably could and measured the lengths of the line around the rectangle. Factors in the difference between the length of the 6 unit line (I should have made it 6 to get it all more accurate) and applied that to the rectangle’s lines and got about 8.35.
And was very wrong somehow.