Mattresses??

So I'm looking through the never ending list of crib mattresses & can't figure them out (pregnancy brain)
Are they all meant to fit a standard size crib? Are they all essentially the same? Any one have any tips bc I am so lost! lol

I'm PRETTY sure they mainly all fit a standard sized crib. My daughter didn't have a real crib until she was a yr old. I got it off of craigslist and went through a couple mattresses and had to return them because non of them fit properly in her crib and I have no idea why. It was an ikea crib and it wasn't like the ones you buy at walmart or BRU so I guess it's measurements were a bit off. If you look at your crib it will tell you the measurements of mattress you need.

Great..thank you so much!! Crib has been ordered so all we need is a mattress so she can actually sleep on it! lol

*watching. Lol I was JUST looking online at mattresses too and I have no clue what's the difference or what's better.