In fact, this is one of the most popular questions when it comes to buying a crib, which is why I decided to tackle this question in a Frequently Asked Question post.
The production of crib mattresses is actually controlled by the Federal government in that the mattress must be 27.5″ x 52″ and it can’t be thicker than 6 inches. This is referred to as a standard mattress size.
The thing to remember though is that there is a little bit of wiggle room when it comes to these measurements. This doesn’t mean that a manufacturer can produce a mattress that is 54″ in length instead of 52″ but it does mean it could be 51.75″.
Most of the time you will notice that it won’t make a difference once you put the mattress in the crib. The important thing is that when you place the crib mattress in the center of the crib platform there should not be more than two fingers of space between the mattress and the side of the crib.
When it comes to the depth of a crib mattress you will have a bigger variation due to the different types of mattresses that you can buy. But as mentioned a mattress can’t be thicker than 6 inches.
Coil crib mattresses tend to be thicker and will most likely be the ones that you find with a 5 or 6 inch depth. On the other hand foam crib mattresses are usually thinner at around 4 or 5 inches. When buying your mattress remember that a firm mattress is preferred over soft ones due to safety concerns.