The right size crib mattress ensures the safety of your little one because it fits snugly against the sides of the crib and prevents gaps. This keeps your child from becoming wedged between the crib and the mattress. The right mattress size and shape also depends on the type of crib you have. To help determine the best – and safest – sleeping experience for your baby, follow our guide to pick the correct crib mattress size.

Types of Crib Mattress Sizes
How to Measure a Crib for a Mattress

Types of Crib Mattress Sizes

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The right crib mattress size should fit snugly inside a crib and accommodate the crib's shape to prevent gaps between the sides of the crib and the mattress edges. Review each size to determine the best one for your crib type:

Standard Crib Mattress Size

The standard crib mattress size is 52" L x 27" W. The mattress is typically 5" – 6" thick and should not be thicker than 6". These mattresses are usually rectangular and are designed to fit snugly inside USA-standard full cribs, which have dimensions averaging within 5/8" of 52" L x 28" W. There should be no gaps larger than two-fingers wide between the mattress and the crib.

Mini Crib Mattress Size

Mini or portable cribs are more cost-conscious and work well in tight spaces. The standard mattress size for a mini crib is 38" L x 24" W. The thickness tends to be lower, around 3" – 4" high and no higher than 5". Just like a standard crib, the gaps between the crib mattress and the sides of the crib should be no more than two-fingers wide. Mini crib mattresses are usually smaller rectangular- or square-shaped compared to standard crib mattresses.

Cradle Crib Mattress Size

Cradles can vary in size but standard cradles can accommodate a mattress that measures 36" L x 18" W. These mattresses usually have 1½" thickness to maintain a firm, safe sleeping space for babies to sleep comfortably. They also come in oval or rectangular shapes to accommodate different cradle designs.

Bassinet Crib Mattress Size

Bassinets are smaller than cradles and mini cribs, so they require smaller mattress sizes to fill out the space. Bassinet mattresses typically measure 30" to 33" L and 15" to 18" W. Like cradle mattresses, they have a thin but firm composition that is 1½" to 2" thick. This prevents the mattress from sinking with the weight of the baby and promotes healthy breathing while sleeping.

How to Measure a Crib for a Mattress

There are a few key steps to take to determine the right mattress size for your crib.

1. Review Your Crib's Product Manual

Start here if you have your crib's product manual on-hand to reference. Most crib manuals should list compatible mattress sizes and types so you don't even need to take your own measurements. You can also determine compatible mattress sizes for your crib by going to the crib's product page and taking a look at the “You Might Also Need” section below the Add to Cart button.

2. Measure the Crib's Interior Length & Width

If you don’t have your product manual, or can't find compatible mattress information, don't worry! The crib mattress measurement process is quick and simple. Take a tape measure and place it on the inside of the crib. Measure across the interior of the long side of the crib to the other side to determine the correct mattress width. Then measure from the interior of the short panel on the end of the crib to the one directly across from it. This should measure the length of the crib and the length of the compatible mattress size.

3. Subtract a Half Inch From Your Measurements

As a general rule of thumb, there shouldn't be more than 1 inch of space between the crib and the crib mattress or more than two finger-lengths. Subtract a half inch from the total length and width of the crib to determine a good mattress size. This helps ensure that you can easily lift and lower the mattress into the crib, while also making sure the mattress fits snugly against all sides of the crib.

Tip!

Don't have a crib just yet? Check out our crib dimensions guide to help determine the right size for your nursery, or browse for cribs that already come with a compatible mattress to give you peace of mind.

Learn more about crib safety features and guidelines in our Baby Crib Buying Guide.

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