What Size Is a Crib Mattress?

Published by 
Jess Miller
Last updated: 
March 8, 2023

Did you know that not all crib mattresses are the same size? Just take a stroll down the aisle where they're on display, and you'll notice some slight differences. That's why answering the question "what size is a crib mattress" isn't so cut and dried.

What Size Is a Crib Mattress?

Although crib mattresses can vary in size, regulations state that standard state crib mattresses must be a minimum of 27 1/4 inches by 51 1/4 inches. Furthermore, the thickness must not exceed 6 inches. These standards are in place to help prevent head entrapment as well as suffocation between the crib sides and mattress.

Different Types of Cribs

There are over 30 variations of crib styles to choose from nowadays. However, many are classified as standard or mini. For this reason, it's essential to understand the differences before deciding on one or the other.

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Standard crib

Standard cribs are also known as full-sized cribs. These cribs have interior measurements of 28 inches in width and 52 3/8 inches in length. These measurements were taken into consideration when regulating crib mattress size.

Since standard cribs and mattresses are regulated, a lot of the guessing is taken out of the equation when finding a mattress. Moreover, finding the bedding you want is also easier. Take all that into consideration, and it's no wonder these cribs are more common.

Mini crib

If space is an issue, mini cribs may be the right choice for your lifestyle. However, it's important to keep in mind that mini cribs do not follow strict regulations like standard cribs. These cribs come in all sorts of shapes and sizes.

While some mini cribs can be similar in shape to a standard crib, they are significantly smaller. Most rectangular mini cribs have an interior measurement of 24 inches in width and 38 inches in length. When purchasing a mini crib, pay attention to the dimensions given by the manufacturer and choose your mattress size accordingly.

Choosing a Crib Mattress: Important Considerations

Safety should be our first concern when it comes to choosing the best mattress for your baby. Unfortunately, babies face more safety concerns than just head entrapment. With that being said, there are other factors to consider besides the mattress dimensions.

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No matter what type of crib you choose, it's important to double-check the fit of the mattress. One way to check before purchasing is to place the mattress in a display crib. This will help save you a trip back to the store later.

If you're unable to do that, you can use the two-finger rule. After placing the mattress in the crib, slide your fingers between the side of the crib and the mattress. If you can fit more than two fingers, then you will need a larger mattress.


When it comes to babies, the firmer the mattress, the better.

Their bodies need more support for their growing bones, as well as resistance for developing and strengthening their muscles. Moreover, if the mattress sags downward, this could make it more difficult for the baby to roll back over onto their back. Thus, increasing the chances of suffocation.

According to Consumer Reports, the best way to test firmness is to press down on the middle and edges of the mattress. If it bounces right back up, you're golden.

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What Size Is a Crib Mattress: Answered

Unfortunately, when it comes to crib mattresses, one size does not fit all. However, if you choose a standard crib, you can purchase a standard crib mattress since these have strict regulations. Ultimately, when it comes to choosing the right size mattress, referring to the manufacturer guide is always a good idea.

Have you already purchased a crib and a mattress? Drop a comment below and tell us about your experience.

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