I don't know, man. That's your own call. If it's average size or above, then there will be no need to bring it up before marriage. If it's small/below average, then it's really up to your own judgement. It can be an awkward conversation to have for sure, but if you can't have awkward conversations with the person you hope to marry, that's not good! When and how to bring it up will also be your own call.

I will also add that if you're watching porn, then you really need to stop. Porn exaggerates a lot of things about sex including penis size, pleasure/orgasm, etc. A lot of unrealistic expectations!! As someone already mentioned, sex is less about size and more about technique/ how you use what you got! Also, women are not a monolith. Some women actually prefer smaller/average sizes because bigger ones can be painful. There is no clear cut answer to this.