Measuring girth wrong for years? Can I use pump cylinder size?

Every time I measure girth I’m around 4.5 inch in circumference, but I pack my 1.75 inch cylinder absolutely no problem at the start of a pumping session. I’m not great at math, but a 1.75 inch cylinder translates to 5.5 inch circumference right? Have I been measuring wrong for years? Is the 1.75 inch diameter measuring the inner part of the tube or outer part?

Verify the cylinder yourself, with a ruler, rather than going by its published specs, which are often wrong.

Yes, 1.75 diameter = 5.5 circumferance.

Ya the inner diameter definitely measures 1.75 inches. I guess what I’m getting at is the 5.5 inch girth out of the tube doesn’t feel that big.

I would say the most accurate way to measure would be a tailor’s tape. I bought mine at the supermarket for $5.

There’s also the traditional "strip of paper" method. Cut a strip of paper, wrap it around your shaft, mark the overlap with a pencil, and then use an ordinary ruler to measure the distance between the marks.