A Guide to the Standard Crib Mattress Size

Safety depends on getting the right size crib mattress and proper fit

Baby smiling in cot.
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Shopping for the right crib and mattress is an important step in ensuring the safety of your newborn. The dimensions of full-size cribs and mattresses are set by federal regulation. But there are also non-full-size cribs that are either larger or smaller and must be sold with their mattress included.

The purpose of the regulations is to prevent head entrapment and suffocation between the mattress and crib sides.

They were enacted by the Consumer Product Safety Improvement Act of 2008 and went into effect in 2011.

Crib Mattress Dimension Standards

The minimum size of 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 interior dimensions ranging from 27 3/8 inches to 28 5/8 inches wide and from 51 3/4 inches to 53 inches long. The crib, its retail carton, and the assembly instructions must have the dimensions listed for the required mattress size.

If a crib has a non-standard size, it must be sold with the mattress included. When it is placed in the center of the crib, there can't be a gap of more than 1/2 inch at any point. If it is placed against one side, there can't be a gap of more than 1 inch at any point.

What to Look for in a Full-Size Crib Mattress

You will see a slight variation in width, length, and depth among full-size crib mattresses as the standard for length and width prescribe a minimum, not an exact measurement.

Before heading to the store or ordering online, check the warning label on your crib to find the exact measurements required for its mattress.

  • Width and length: In both the U.S. and Canada, a full-size crib mattress may range from 27 5/8 inches to 28 5/8 inches wide and 51 3/4 inches to 53 inches in length.
  • Depth: The depth of the crib mattress can vary even more. Coil crib mattresses tend to be on the thicker side—between 5 inches to 6 inches—whereas foam crib mattresses are more on the order of 4 inches to 6 inches.
  • Firmness: Keep in mind that a firm mattress is preferred over soft mattresses. In fact, the firmer the better. Soft sleeping surfaces create a suffocation hazard for infants and increase the risk of SIDS—the leading cause of death in infants in the United States. Put it to the test. Press on the mattress in the center and at the edges. Does it snap back readily?
  • Fit: It's 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 and could lead to suffocation or entrapment.
  • Price: 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. According to Consumer Reports, a good quality mattress can cost anywhere from $90 to $200.

Crib Mattresses and Safety

When you want to replace the mattress in your crib, check the warning label on the crib that lists its mattress size.

If you don't see a label, it's an indication that it is an older crib or one that was modified. That can mean that it doesn't meet the newer safety regulations and you may want to consider getting a new crib. The Consumer Product Safety Administration recommends that you don't use cribs older than 10 years old.

If you buy a mattress and discover that it doesn't fit your crib correctly, you should return the mattress and buy one that has larger dimensions. A gap is a safety hazard.

A Word From Verywell

When you set up your nursery, the crib and its bedding are the centerpieces. Guidelines for reducing the risk of SIDS includes using a firm, well-fitted mattress with a fitted sheet and eliminating any pillows, comforters, or soft objects.

By buying the correct size mattress, you will help keep your infant safe.


Full-Size Baby Cribs Business Guidance. Consumer Product Safety Commission. https://www.cpsc.gov/business--manufacturing/business-education/business-guidance/full-size-baby-cribs.

Non-Full-Size Baby Cribs Business Guidance. Consumer Product Safety Commission. https://www.cpsc.gov/business--manufacturing/business-education/business-guidance/non-full-size-baby-cribs.

Safe to Sleep - Crib Information Center. Consumer Product Safety Commission. https://www.cpsc.gov/Safety-Education/Safety-Education-Centers/cribs/.

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