I'm sorry if this wouldn't be considered appropriate content, but I didn't really another place to go since r/ sex disabled my post for being about cock size.

So me and a girl were considering to have sex sometime soon, which would be the first time for us both. So just in case it would come up randomly I wanted to be prepared but I got into some problems when looking for condoms. I know I'm a girthier than average so I was looking up how to get the right condom and they told me to first measure my girth and then calculate that into the width.

So I started by measuring at first I did it with a piece of paper, but when I ran into problems I did it again twice more, once with string and once with measuring tape (the one that's used with sewing). For all three ways I got 18cm/7inch.

So then I went on to calculate width in two ways, by dividing by two and dividing by Pi. The method of dividing by two was most commonly mentioned but Pi seemed to make way more sense to me. which way is the right way?