Cupid
Most of them are universal, but just in case, it's always a good idea to carry a measuring tape in your purse. You can also compare dimenstions online for most products. I purchased the Ellis 4-in-1 crib with the Sealy crib mattress, it fit perfectly. Best Wishes. ;-)

667mom
if they are for a crib they all fit. I personally don't think you need to spend a lot of money on this. They are only on it a couple of years. Wal-mart or any baby store. If you buy a used one clean it with a clorox solution rinse well dry off and use a plastic mattress cover under the fabric one.

Leana K
As long as you're not buying anything vintage, then the cribs and mattresses are all standardized now and will fit. I always use a plastic mattress with a nice mattress pad over it. Baby diapers don't always contain the poo, so it's important to be able to wash everything and not retain bacteria in the mattress.

coopermom2006
Almost all certified crib mattresses are the same size, there may be a centimeter of difference. I would wait until you get a crib to buy the mattress, in case the crib is a bit different size, or at least make sure that you can exchange the mattress if you buy it before hand and it doesn't fit. I would try to get a mattress with a plastic like coating and vent holes (most baby/toddler mattresses are like this anyway) and some protective sheets for the mattress. I bought my mattress at Babies R Us, and the crib came from EBay. Good Luck!

Ally K
Discount stores carry mattresses, but I understand that certain brands like Colgate (are they the same people that make toothpaste?) rate highly in the reviews. There are certain tests that a crib mattress must pass before it's considered safe in your crib, so the only sure way to know would be to buy it and put it in the baby's bed to be sure that it fits like it's supposed to.

♥Draigh's Mommy!!
Most of them are a "standard" size and so when you're buying a crib just make sure it says "uses standard size crib matress". You'll be able to tell the ones that aren't standard size from the others. You'll see some that are much smaller...those are use primarily for portable cribs.