What is the standard crib mattress size?

The standard crib mattress size is 27 ¼ inches x 51 ⅝ inches with a thickness not to exceed 6 inches. This standard was put in place by the Consumer Product Safety Improvement Act of 2008 that went into effect in 2011. The Act includes regulations for infant and toddler products, such as bedding and toys. The standard mattress size helps to prevent entrapment and suffocation between the mattress and crib rails.

Because both cribs and mattresses fall under this regulation, you can confidently buy them separately, knowing they'll fit together. The regulation is for full-size cribs only. If you're buying a non-full-size crib, a coordinating mattress must be included.

Dimensions of your crib and mattress should be listed on the packaging and the assembly instructions. Your full-size crib should have interior dimensions between 27 ⅜ - 28 ⅝ inches in width and an interior length between 51 ¾ - 53 inches. With these parameters, a standard crib mattress will fit safely in your crib. Non-standard crib mattresses can vary in size and shouldn’t be used with a full-size crib.

How should a crib mattress fit?

Your crib mattress should fit snugly in the crib, without a gap of more than an inch at any point on any side. To test the fit, use a ruler or place two fingers between the mattress and crib sides. If the gap is larger than an inch or your two fingers, the mattress is too small and poses an entrapment and suffocation risk for your little one. If you're using the standard crib mattress size in a full-size crib, you shouldn’t have a problem. Remember to only use crib-specific mattresses—no other cushions or foam pads should be put in the crib.

Besides ensuring the fit is right, take time to build your crib properly. Follow the assembly directions for the crib and don’t use cribs older than ten years, or ones with broken parts. Making an investment in a safe spot for baby pays off for months and years to come.

What should I look for in a crib mattress?

Besides getting the proper crib mattress size, watch for a few key factors to ensure the comfiest and safest spot for your babe to rest their head. 

Firmness

Your baby’s mattress should feel firm and sturdy, not soft and squishy. Soft mattresses can cause suffocation and increase the risk of sudden infant death syndrome (SIDS). To test the firmness of your mattress, press into it. The material should immediately rebound to its original position. 

Depth

Your mattress should be six inches or less in depth. Mattresses with coil springs usually measure between five and six inches while foam mattresses tend to be between four and six inches deep. Choose the depth and material that feels most comfortable to you. If it's a mattress you'd sleep on, chances are your little one will too.

Weight

Foam mattresses tend to weigh less than coil spring mattresses—making it easier to change the cover and sheet. 

Length of use

Federal regulations warn against using any mattress or crib that’s over ten years old. If you keep your mattress in good condition, you can use it for several children. Note that cribs are usually designed for children under three years old. Some crib mattresses are reversible, or two-staged. If your mattress is, follow the instructions or talk with your pediatrician about when it’s time to flip your mattress from the infant side to the toddler side.