I have a Valentine gift for y'all :
here it is.
It's an online excel table which lets you calculate a poll's margin of error, a particular score's range within that margin of error (the MoE is not the same for a score of 50% or 12%), the margin of error of a subsample and a particular score in that subsample's range. Also, you can input an MoE and it will give you the sample size used.
I wasn't sure where to put it, so I posted here directly for use with polls, but a mod can transfer it elsewhere. The table is modifiable online, but I'll advise you to download it and use it locally, because it's just the one table for everyone to use.