How to Choose a Crib Mattress

Getting the Correct and Safest Fit

Standard crib mattress size
Illustration by Joshua Seong. © Verywell, 2018.

One of the most delightful parts of expecting a baby is putting together the nursery. It's also one of the most important. While the perfect paint shade and cutest bedding and most inviting toys matter, so do features like a safe crib and changing table.

Among the list of items parents-to-be should consider carefully is the crib mattress. It's where a baby will spend at least several years and can make a big difference in how comfortable—and safe—she is.

Crib Mattress Safety Standards

Because safety is central to choosing a crib and mattress for a newborn, the dimensions of full-size cribs and mattresses have been standardized under federal regulations. That makes it easy to buy the two separately without worrying about fit. 

The same rule doesn't apply to non-full-size cribs. however. Therefore by law, these must be sold with the mattress included.

The aim of these 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.

Size Matters

A full-size crib mattress must be at least 27 1/4 inches wide and 51 1/4 inches long and no more than six inches thick. At these dimensions, the standard crib mattress will fit safely in a 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. These dimensions and those of the mattress must be 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 make certain you purchase a mattress with the exact measurements needed.

Other things to consider:

  • As a rule, firm mattresses are better for babies than overly-soft ones. In fact, the firmer the better. Soft sleeping surfaces create a suffocation hazard for infants and increase the risk of 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 five inches to six inches deep—whereas foam crib mattresses are closer to four inches to six 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 between $90 and $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, replace the crib entirely. The Consumer Product Safety Administration recommends never using a crib that's older than 10 years.

    If you buy a mattress and find 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.

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    Article Sources
    • ASTM F1169-13, "Standard Consumer Safety Specification for Full-Size Baby Cribs." ASTM International. West Conshohocken, PA; 2013.
    • ASTM F406-15, "Standard Consumer Safety Specification for Non-Full-Size Baby Cribs/Play Yards." ASTM International. West Conshohocken, Pennsylvania; 2013.
    • Consumer Product Safety Commission. "Safety Standards for Full-Size Baby Cribs and Non-Full-Size Baby Cribs; Final Rule." Bethesda, Maryland; Dec 28, 2010; document citation 75 FR 81765.

    • Consumer Reports. "Crib Mattress Buying Guide." April 2016.