We try to provide guidelines for each piece on its product page. If you don't see a guideline and are unsure if your message will fit, please contact us and we are happy to help. The examples we show on the product page should also hopefully guide you on how many words will fit on a piece.
The more words you put on a charm, the smaller the handwriting ends up. But many words in small handwriting can still look really nice on a charm or ring or bracelet.
For example, we have done a couple words on a guitar pick and it looked great. We also have done entire letters on a pick and while the writing was small, it was readable and looked amazing. Please see examples attached here. But again, if you are still unsure if something will fit on a charm, please contact us!