Just 3 steps to success!
Look very closely at the bar on the condom package.
Think about your penis when it's hard: is it about the same width?
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 refrain from actually comparing your penis to the pack in the store. This would be unhygienic and could get you into trouble. Instead of physical work, real mental work is required here.
So that you can try it out in peace, we recommend one of our practical Test Packs that contain three different, but similar sizes. You should be able to feel which condom size is right for you.