How Big Are Crib Mattresses?

Crib Mattress Sizes and Dimensions

Standard Size

The standard crib mattress is designed to fit a full-size crib snugly, ensuring your child's safety. According to the US Consumer Product Safety Commission (CPSC), standard crib mattresses should have a minimum dimension of 27 1/4 inches in width, 51 1/4 inches in length, and a maximum thickness of 6 inches. Full-size cribs 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.

It's worth noting that standard crib mattresses typically measure 28 inches by 52 inches. The mattress bases in standard cribs can be lowered as your child grows, making it a lasting piece of furniture for them to sleep in.

Mini Size

Mini cribs are a space-saving alternative, and as such, they require smaller mattresses. Mini crib mattresses usually measure 24 inches in width and 38 inches in length. These mattresses are ideal for smaller nurseries, for families who travel frequently, or for those looking for a temporary sleep solution for their babies.

When selecting a crib mattress, it's essential to measure the crib to ensure the mattress will fit correctly, as this directly impacts your child's safety and comfort.

Materials and Thickness

When it comes to crib mattresses, there are two primary types of materials used: foam and innerspring. Each material has its own advantages and disadvantages, and understanding these differences will help you make the best choice for your baby's comfort and safety.

Foam Mattresses

Foam mattresses are made from a variety of materials, including polyurethane, memory foam, and latex. They are typically lighter in weight and provide good support for your baby. The thickness of a foam mattress can range from 3 to 6 inches, with the standard crib mattress size being no more than 6 inches thick.

When selecting a foam mattress, consider the following:

  • Density: A denser foam will offer better support and will be more durable. Look for a mattress with a density of at least 1.5 pounds per cubic foot.
  • Firmness: A firmer mattress is safer for your baby, as it reduces the risk of suffocation. Press on the mattress to ensure it springs back quickly.

Innerspring Mattresses

Innerspring mattresses have a core of steel coils (also called springs) that provide support. These mattresses tend to be heavier and can be more expensive than foam mattresses. The thickness of an innerspring mattress also ranges from 3 to 6 inches, with standard size guidelines to ensure a safe fit in a crib.

When choosing an innerspring mattress, keep in mind the following:

  • Coil count: A higher coil count generally means better support and durability. Look for a mattress with at least 135 coils.
  • Gauge: The gauge refers to the thickness of the steel coils. A lower number indicates a thicker gauge and firmer support. Opt for a gauge between 15.5 and 17.5.

Both foam and innerspring mattresses come with various coverings, such as water-resistant or hypoallergenic options, which can be important for a baby's health and comfort. Make sure to evaluate the materials and specifications before making a final decision on a crib mattress.

Compliance with Regulations

Safety Standards

The U.S. Consumer Product Safety Commission (CPSC) has set new federal mandatory safety standards for crib mattresses, ensuring a safer sleeping environment for babies. These standards cover crib mattresses, including after-market mattresses used in play yards and cribs. Full-size crib mattresses must be at least 27¼ inches wide and 51⅝ inches long, with a corner gap not exceeding 3.15 inches when used with a test mattress sheet, as specified in the CPSC guidance.

It's crucial to note that cribs made before July 2010 may not meet these safety standards and should be replaced. For cribs purchased after July 2010, it's essential to check their compliance with the new safety requirements to ensure the safest sleep environment is provided. This includes a ban on drop-side cribs, as detailed by aBaby's guide.

Flammability Requirements

Flammability requirements are also an essential consideration in crib mattress regulations. Full-size baby cribs must comply with the full-size crib standard, which includes the Consumer Product Safety Improvement Act of 2008 (CPSIA). More details about these standards can be found on the official CPSC website.

Choosing the Right Fit

When selecting a crib mattress, it's crucial to choose one with the proper dimensions to ensure your baby's safety. A full-size crib mattress should be at least 27 1/4 inches wide, 51 1/4 inches long, and no more than six inches thick. This standard size ensures a snug fit in most full-size cribs, which can vary slightly in their interior dimensions.

Gap between Mattress and Crib

It's essential to pay attention to the gap between the mattress and the crib's sides. A narrow gap is crucial for your baby's safety, as a larger gap could potentially pose a risk of entrapment. According to the American Academy of Pediatrics (AAP), the mattress should fit tightly in the crib, leaving no more than two fingers' width between the mattress and the crib's sides.

To ensure the mattress fits properly, measure the crib's interior dimensions and compare them to the measurements of the mattress. Remember, a well-fitted crib mattress not only makes the sleep environment safer for your baby but also allows for a more comfortable and supportive sleep.

Using the proper crib mattress size and ensuring a minimal gap between the mattress and crib sides will help you create a safe and comfortable sleeping space for your baby. By paying close attention to the fit, you'll be confident in making the right choice for your little one's restful slumber.

Benefits of Proper Crib Mattress Size


A properly sized crib mattress can significantly enhance the safety of your baby's sleeping environment. The appropriate size for a crib mattress is at least 27 1/4 inches wide by 51 1/4 inches long. This specific measurement helps ensure that there is no dangerous gap between the mattress and the crib frame.

According to the "two-finger" test, there should be no more than two finger-widths of space between the side of the mattress and the crib frame. Larger gaps could pose a risk of entrapment, which is a serious hazard for infants.


In addition to safety concerns, a well-fitted crib mattress plays a crucial role in ensuring your baby's comfort. Too tight, and the mattress might be compressed, causing it to lose its shape and firmness. On the other hand, if the mattress is too small for the crib frame, there is the risk of your baby rolling to one side and getting caught between the mattress and the crib.

Moreover, the thickness of a crib mattress should ideally be no more than six inches, which helps promote even distribution of your baby's body weight, offering greater comfort during sleep hours.


Finally, a properly sized crib mattress offers convenience for parents in terms of:

  • Sheet fitting: It's much easier to find and fit sheets for a standard-sized crib mattress than for an unusual or custom size.
  • Upgradability: If the crib mattress follows the standard size requirements, upgrading to a larger bed as your child grows becomes more seamless and requires less effort.
  • Durability: A crib mattress of the right size and type, such as memory foam or innerspring, can have a longer lifespan and remain in good condition throughout your child's early years. Choosing a well-suited mattress will ultimately result in a better investment in the long run.

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