Comment by FinnKuhn

German postage for letters is under 20g, under 50g and under 500g so I had this issue a few times so far when sending a few letters a day over a few weeks. You can see it here for international letters for example: https://www.deutschepost.de/en/b/briefe-ins-ausland.html

Thankfully I just had a scale, but I can see this being helpful when you don't.