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Crib Mattress Size Guide

Crib Mattress Size Guide

A baby can spend up to 18 hours a day in the crib. For this reason, parents need to pay special attention to this element when designing a nursery. Selecting an appropriate crib mattress is arguably the most essential part of purchasing a crib since it directly affects the baby’s comfort and safety. While other factors can play an important role, the first step should always be selecting the right crib mattress size.

This guide will walk you through the different cribs and the corresponding crib mattress sizes available on the market. Plus, we’ll go over how a crib mattress should fit so you can make an informed decision, keeping your little one’s best interests at heart.

How Should a Crib Mattress Fit?

You’ll know the crib mattress dimensions are ideal for your crib if you can’t fit more than two fingers between the mattress and the crib frame. If you’re solely looking into the crib mattress dimensions, make sure that the crib mattress length and width aren’t over one inch smaller than the crib’s dimensions.

Besides the width and length of a crib mattress, you should pay attention to the crib mattress thickness or height. A crib mattress shouldn’t exceed six inches in height, measured from seam to seam. If the mattress is higher, the baby will be able to climb out of the crib as it grows.

Appropriate shaped, mini, and standard crib mattress dimensions are crucial for ensuring the baby is safe within the crib.

If the mattress is too small, the baby can get stuck in the gap between the mattress and the crib. This increases the chances of suffocation. This worst-case scenario can also occur if the mattress is slightly bigger than necessary, making it bulge in the middle.

Are Crib Mattresses All the Same Size?

Not all crib mattresses are the same size. The mattress size varies based on the type of crib parents choose. Generally speaking, there are three types of cribs: standard, mini, and shaped. Only standard cribs have regulated interior dimensions, while mini cribs differ slightly from one brand to another. In contrast, shaped cribs significantly differ in design depending on the brand, and their crib mattress measurements follow suit.  

Standard Crib Mattress Size

Standard crib dimensions are dictated by ASTM (American Society for Testing and Materials) and federal law. According to them, a standard-sized crib must have interior dimensions of 28 inches wide and 52 3/8 inches long. These dimensions can vary by 5/8 inches at most.

Standard crib mattresses are designed to be slightly smaller than these dimensions, allowing them to fit appropriately within the crib. Still, this mattress shouldn’t be too small since a gap between the mattress and the crib can be a safety hazard for the baby.

With this in mind, the dimensions of a standard crib mattress should be at least 27 1/4 inches wide and 51 1/4 inches long. The gap between the mattress and the crib shouldn’t surpass one inch.

Since there’s a little wiggle room even with a standard-sized crib, parents should measure the interior dimensions of their desired crib before purchasing a standard crib mattress.

Standard cribs are generally the go-to choice for most parents. They are more expensive than mini cribs but can also easily convert into toddler beds. Therefore, the child can use them for several years, making them a wise investment.

Mini Crib Mattress Size

As the name suggests, a mini crib is smaller than a standard-sized crib. The dimensions of mini cribs aren’t regulated by law. However, most brands manufacture mini cribs of similar sizes, with only slight differences. In general, mini cribs are 24 inches wide and 38 inches long.

Naturally, these cribs require corresponding mini crib mattresses. Luckily, most mini crib mattresses on the market will fit a 24-inch by 38-inch mini crib. Still, it would be best to double-check to ensure the gap between the mattress and the crib isn’t larger than one inch.

Some parents decide to purchase a mini crib since it’s easier on the wallet. However, you should keep in mind that your baby will outgrow the mini crib relatively quickly, so you’ll have to spend money on another bed to fit your growing toddler.

The price isn’t the only attractive feature of these cribs. Their compact size comes in handy for nurseries that are short on space. Also, they’re ideal for babies who share a bedroom with an older sibling or a twin brother or sister. Or if you have twins.

You can even purchase a mini crib to have on hand when traveling or visiting friends and family members. This way, overnight stays will be more comfortable and convenient.

Shaped Crib Mattress Size

A standard-sized crib is always rectangular. The same goes for its mini counterpart. So, parents who want to add a unique design element to the baby’s nursery typically go for a shaped crib mattress size. Most shaped cribs come in round, oval, or hexagonal shapes.

Since no government regulations dictate the size of shaped cribs, the same goes for shaped crib mattresses. Most shaped cribs come with a matching mattress to make the purchasing process more straightforward.

If your desired crib isn’t sold with a mattress, you’ll have to measure it to determine the correct mattress dimensions. As always, the same rule applies: not too big or too small.

Use a tape measure to determine the crib’s size, and then look for a mattress that will fit snugly inside the crib without leaving too much wiggle room around the edges. Shaped cribs typically call for mattresses smaller than standard crib mattress dimensions.

Shaped cribs allow parents to get creative with the nursery, but they can often be rather costly. If the cost doesn’t pose a problem, a shaped crib is perfectly safe for the baby, provided it contains a correctly-sized mattress.

The Bottom Line

baby on mattress

The baby mattress size should be the first aspect to consider when looking into crib mattresses. However, parents shouldn’t purchase a crib mattress solely based on size. Other important factors to keep in mind include how firm, breathable, and durable the desired mattress is. As it’s an essential item you can never be too careful when choosing the best crib mattress. So, make sure to thoroughly research all these aspects before making the final decision.

Jessica Daniels

Hey there! I’m Jessica Daniels, the owner of Posh Tots and a proud mom of two.

Me and my team of experts (who also happen to be moms) test and review parenting products, and share our tips and tricks to help you make informed choices for your little ones.

Let’s navigate this crazy parenting journey together!

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