Just 3 steps to success!
01. look
Look very closely at the bar on the condom package.
02. estimate
Think about your penis when it's hard: is it about the same width?
03 Enjoy
If yes: Congratulations, you have found your personal condom size and can try it directly. If no: Take a pack in another size and start again with step 01.
PS: Please don't get the idea to hold your penis to the pack in the store. That would be unhygienic and could get you into trouble. Here, instead of manual labor, real mental work is required for once.
So that you can try it out in peace, we recommend one of our practical trial sets with three different, but similar sizes. You can feel which one belongs to you.