How to Choose a Crib Mattress

Selecting the Safest One Whatever the Crib Size

Baby smiling in cot.
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Expecting parents will spend a lot of time preparing for the new arrival by ensuring they get the safest crib, the softest bedding, and the cutest crib toys imaginable. In some cases, the last thing they will think about is the mattress.

But it is the mattress, in fact, that is one of the most important features of the nursery. It is not only where your baby will spend the greater part of the next few years, it can make a big difference in how comfortable—and safe—your baby is.

Crib Mattress Safety Standards

Safety is central to the choice of the right crib and mattress for your newborn. To this end, the dimensions of full-size cribs and mattresses have been standardized under federal regulations so that you can buy either separately and still have a perfect fit.

That same doesn't apply to non-full-size cribs. By law, these must be sold with the mattress included.

The aim of the regulations is to prevent accidental head entrapment and suffocation between the mattress and the crib sides. The laws were enacted by the Consumer Product Safety Improvement Act of 2008 and officially went into effect in 2011.

Crib Mattress Dimension Standards

A full-size crib mattress must be at least 27 1/4 inches wide and 51 1/4 inches long. It must not be thicker than 6 inches deep. This is designed to fit the full-size crib, which can have an interior width of between 27 3/8 inches and 28 5/8 inches, and an interior length of between 51 3/4 inches to 53 inches.

The crib must have its dimensions and those of the mattress listed on both the retail carton and assembly instructions.

Obviously, non-standard crib mattresses can vary in size. When one is placed in the center of the crib, there cannot be a gap of more than a half inch at any point. If it is pushed to one side, there cannot be a gap of more than an inch at any point.

Again, this shouldn't be a worry for consumers, as non-standard cribs and mattresses are sold as sets.

What to Look for in a Full-Size Crib Mattress

Since the federal regulations dictate an acceptable range in mattress dimensions, there can be a slight variation in the width, length, and depth. Before heading to the store or ordering a mattress online, check the label on your crib to ensure you get a mattress with the exact measurements needed.

Other things to consider:

  • As a rule, firm mattresses are preferred over soft mattresses. In fact, the firmer the better. Soft sleeping surfaces create a suffocation hazard for infants and increase the risk sudden infant death syndrome (SIDS). One way to test firmness is to press on the mattress in the center and at the edges. When you release it, it should snap back immediately.
  • Mattress depth doesn't necessarily translate to mattress firmness. Coil-spring mattresses tend to be on the thicker side—between 5 inches to 6 inches deep—whereas foam crib mattresses are closer to 4 inches to 6 inches deep.
  • It is also important to focus on whether the crib mattress is centered on the platform and fits snugly in the crib frame. A good rule of thumb is that if you can squeeze more than two fingers between the side of the mattress and the crib frame, the mattress is too small.
  • While you don't want to cut corners when it comes to buying a crib mattress, you also don't have to blow your entire nursery budget either. According to Consumer Reports, a good quality mattress will cost anywhere from $90 to $200.

Crib Mattresses and Safety

When you need to replace the mattress in your crib, always check the warning label on the crib for the correct dimensions. If you don't see a label, it may be that the crib is either older or has been modified. If in doubt, it is best to replace the crib entirely. The Consumer Product Safety Administration recommends that you never use a crib older than 10 years.

If you buy a mattress and find that it doesn't fit correctly, return it immediately and get another one that does. Never try to "make do" by shoring up the edges with fabric or foam. Anything other than a snug fit should be considered a safety hazard.

In this regard, while online shopping may be convenient, you may be better served shopping for mattresses at a brick-and-mortar store. You can then do a proper check of dimensions and firmness before making a purchase.

A Word From Verywell

When setting up your nursery, take some time to acquaint yourself with the guidelines on how to reduce the risk of SIDS. In addition to buying a firm, well-fitted mattress, you'll need to get properly fitted sheets and eliminate any pillows, comforters, or soft objects that pose a suffocation risk.


ASTM International. "ASTM F1169-13, Standard Consumer Safety Specification for Full-Size Baby Cribs." West Conshohocken, Pennsylvania; 2013; DOI 10.1520/F1169-13.

ASTM International. "ASTM F406-15, Standard Consumer Safety Specification for Non-Full-Size Baby Cribs/Play Yards." West Conshohocken, Pennsylvania; 2013; DOI 10.1520/F0406-15.

Consumer Product Safety Commission. "Safety Standards for Full-Size Baby Cribs and Non-Full-Size Baby Cribs; Final Rule. " Bethesda, Maryland; December 28, 2010; document citation 75 FR 81765.

Consumer Reports. "Crib Mattress Buying Guide." Yonkers, New York; April 2016.