Having a newborn baby is possibly one of life’s greatest joys, but it can also present some of the greatest challenges. One of these potentially headache-inducing aspects of having a baby is choosing the right baby mattress size for your infant.

The level of difficulty this presents depends on where one lives in the world. For example, in the United States, the precise measurements for a full-size baby crib and its corresponding mattress are federally regulated, which leaves buyers with little room for error. This is only for full-size cribs and mattresses though—in all other cases, the mattresses have to be sold together with the cribs in order to make sure they fit one another.

Why is it important to choose the right baby mattress size?

There are some quite real reasons why one should be concerned about their baby mattress size. It is not just a matter of aesthetics or convenience. Rather, your baby can suffer potentially life-threatening hazards from sleeping on a mattress that is too small for its crib.

For example, since infants are quite small, it is easy for them to get stuck in the space between the mattress and the crib. This can easily happen if the mattress is not large enough and could potentially result in physical injury or suffocation. This is why it is crucial to pay attention.

In a way, this is the answer to the core question of this article: the size of your baby mattress should be such that it fits into the crib in such a way so that there are no spaces for your baby to fall into.

Approximately, what does this mean in terms of dimensions?

In the United States, a standard baby mattress size is at least 27 1/4 inches wide and 51 1/4 inches long and no more than six inches thick. This way it can comfortably fit in a full-size crib without leaving any dangerous gaps.

When it comes to non-standard sizes, it is crucial that when the mattress is placed into the crib, that there is not a gap of more than half an inch at any point. When the mattress is pushed all the way to one side, the resulting gab must not be bigger than an inch.

Again, this should not be a worry taking into consideration that, at least in the United States and several other countries, baby cribs and mattresses are sold in sets which means that they will be compatible 99.9% of the time. Regardless, it never hurts to check and make sure your infant does not get hurt.


A baby mattress is not as easy to purchase as one might think. There are several factors to take into consideration, from firmness to its size.

In this article, we have discussed the size aspect and concluded that it is not exactly how big the mattress itself is that is so crucial, but rather its compatibility with the size of the crib. Keep this in mind and make sure your baby does not suffer unnecessary injury.

If you found this article interesting, find our full mattress reviews here!