As an Amazon Associate I earn from qualifying purchases.

What Size is a Standard Crib Mattress?


Babies grow at a pretty quick clip in the first few months and you’ll witness big growth spurts during this time. Eventually, your baby will require a shift to their own crib, even if they’re co-sleeping or in their bassinets right now.  

According to the American Academy of Pediatrics (AAP), you and your baby should be sleeping in the same room at least for the first 6 months if not for the whole year. This means you place your baby’s crib, bassinet, portable crib, or play yard close to your bed, so you’re more easily alerted to any problems your baby will face. This helps promote night-time breastfeeding and reduce the risk of Sudden Infant Death Syndrome (SIDS). 

The first 12 months of a baby’s life is when they undergo explosive growth and this comes with its challenges. As soon as you think you’ve succeeded in putting together some kind of a nap schedule, your baby will outgrow their bassinet and end up waking up more because of bumping into the sides. 

Moving a baby into their own crib is inevitable and can be tricky as it will be a disruption to their routine. The transition from co-sleeping or bassinet may seem challenging as it might cause temporary sleep setbacks as well. 

The crib is an important factor in the overall design of your baby’s nursery and the mattress where your baby spends most of his or her time will have a big impact on your baby’s comfort and safety. But you shouldn’t lose sleep over it, as they’re some things that you as a parent can do to ensure the transition is as smooth as possible for both your baby and yourself.

On the top of the to-do list will be to ensure that the mattress you ultimately buy for your crib is as comfortable, as durable and as safe as possible. You can see how important it is that you choose the right mattress especially when you consider that a child below the age of 3 can spend up to 16 hours each day sleeping. 

It’s crucial your crib’s mattress meets the ASTM safety regulations which stipulate that they fit properly inside USA-standard full-size cribs and toddler beds. It’s important you are aware of the inner dimensions of your crib to ensure that it meets these safety standards.

We’ve done the groundwork to bring you clarity to some of the aspects of cribs and mattresses that parents might find challenging. 

The Crib’s History:

Derived from the Old English word “Cribb”, what was basically a manger in the shape of a bassinette has evolved to the present day high-sided, slatted child’s bed that we call “crib”.

Safety Guidelines:

A 19-year study published in the journal Pediatrics reveals an eye-opening statistic. US emergency rooms treat nearly 10,000 up to 2-year-olds every year for crib, playpens, or bassinet injuries. Of those, roughly 66% of injuries specifically involve babies jumping or falling from a crib, playpen or bassinet. These sobering statistics make it crucial that parents are aware of the potential dangers in your baby’s crib. 

According to the prescribed safety guidelines, you should ensure your baby’s crib (especially when using a hand-me-down) meets the newest safety guidelines and that it is installed correctly and carefully. The current safety standards banned the manufacture and sale of drop-side rail cribs in 2011, so that’s one more important fact to remember when accepting a second-hand crib. 

These safety standards also cover crib mattresses relating to their dimensions. The guidelines recommend a 6-inch thick mattress, to ensure that a crib is “escape-resistant”.

Your child will be susceptible to falling out and suffering injuries as soon as they’ve managed to pull themselves up in her crib. To stop this from happening, the regulations have set the minimum distance between the top of the mattress and top of the crib side rail as 26 in.

Here are Some of the Important Features to Consider Regarding Cribs and Mattresses:

  • Slats of the crib should be no more than 2 3/8 inches (6 cm) apart.  This is to keep your baby safe and prevent untoward injuries. 
  • The mattress should be at least 6 inches thick and needs to be lowered as your child grows. This periodic lowering of the mattress will prevent your infant from climbing or falling out of the crib. 
  • Crib mattresses should be a snug fit in the crib. Any space more than two fingers between the side of the mattress and the crib frame poses a suffocation and entrapment hazard. 
  • With regards to the firmness of a crib mattress, the general rule of thumb applies; firmer the better. As soft surfaces can pose a suffocation hazard and increases the chances of SIDS. 
  • You should avoid using a foam topper or other non-standard crib mattress over it.
  • All screws, bolts, nuts, plastic parts, and other hardware should be present and original equipment. They must be fastened securely and tightly place to prevent the crib from coming apart; a child’s activity can cause the crib to collapse.
  • Weekly inspections for damage to hardware, loose joints, missing parts, or sharp edges are a good thing.

Timing the Move to the Crib:

Transitioning into a crib from bassinet, swing, or bouncy chair can be for a number of reasons. Getting the timing right is what makes the going smooth. Most babies will transition between the 3 months to 6 months mark. Pediatricians do say that parents of faster-growing babies will have to think about the move to a crib even before. 

A small baby at even 8 months old might still be getting decent peaceful sleep time in the bassinet. For them, it makes sense to not rush into transitioning to a crib. 

Here Are Some Guidelines to Time Your Baby’s Transition to the Crib:

  • Your Baby’s Weight

Bassinets and co-sleepers usually have a higher weight limit of 20-pounds. To err on the side of caution move the baby into a crib when they hit 15 pounds.

  • Does your baby look uncomfortable?

If you find your baby suddenly and frequently waking up crying, they might be demanding a little more space. Your decision should ultimately be based on how soundly everyone is sleeping. 

  • Can your baby roll over and move by themselves?

Bassinettes are usually shallower than cribs and the baby might flip over. So if your baby has started to roll and move by themselves, it might be time.

Things to Carefully Consider Before Purchasing a Crib Mattress: 

While shopping for a toddler mattress, ensure it fulfills the following requirements to make sure you’re getting a healthy, safe, and comfortable sleeping surface for your little one. 

According to the mandated federal regulations, there can be a slight variation in the width, length, and depth of crib mattresses. So, before purchasing a mattress, ensure you have the exact measurements by checking the label on your crib.

The inner dimensions of cribs according to the standards require cribs to be 28 inches wide and 52 3/8 inches long. Most crib mattresses are designed to be a snug fit and hence are slightly smaller to allow them to fit within these dimensions.

  • Supportive: Firm mattresses provide better support and comfort than overly soft ones. They also provide the support your baby needs to sleep well and grow healthily. Soft sleeping surfaces pose suffocation hazard for infants and increase the risk of sudden infant death syndrome (SIDS). Test the firmness of the mattress before you buy one.
  • Depth and weight: The depth of a mattress doesn’t necessarily translate to its firmness. Coil-spring mattresses tend to be thicker than foam crib mattresses. Foam mattresses, with the exception of memory foam mattresses, tend to weigh less which makes them easier to lift while changing sheets.
  • Duration of use: Some crib mattresses are dual-purpose and reversible, with a firm side for babies and a softer, more cushioned side for toddlers. Sometimes referred to as “two-stage” mattresses, consult with your pediatrician about when it’s safe to flip the mattress from one side to the other.
  • Breathable: It is a particularly important feature of any crib or toddler mattress. Breathable mattresses allow free circulation of air and let heat escape. This prevents night time overheating which can pose a serious threat for babies and young children.
  • Water-resistant: As any parent will know, babies and toddlers are leaky creatures. A water-resistant mattress prevents unpleasant and harmful liquids seeping into the mattress and making it unsanitary. Many mattresses also come with water-resistant covers that are removable and can be easily cleaned in a washing machine.
  • Certifications: Unfortunately, some mattresses are made using chemicals that could pose a risk to the health of young children, especially if they have a respiratory condition such as asthma. Ensure that your mattresses carry either the Certi-Pur or GREENGUARD Gold certifications. These certifications are given only after the product has been extensively tested to ensure it contains no harmful substances.
  • Hypoallergenic: Mattresses can trigger allergies in many babies and toddlers which can disturb their sleep. For this reason, it’s important you go for a hypoallergenic mattress for your little one.
  • Made in the USA: We recommend that you only consider purchasing crib mattresses manufactured in the USA as they are required to conform to very strict safety regulations. This will ensure that your mattress is safe for your child to sleep on.

The Size of a Standard Crib Mattress:

The US government passed the Consumer Product Safety Improvement Act of 2008 (CPSIA) to federally regulate the manufacture of mattresses to ensure the highest standards of safety and comfort. 

To determine the best sleeping experience for your baby you should buy a mattress that strictly follows these guidelines. You will find these dimensions listed on both the retail carton and assembly instructions. A general rule of thumb is to place your mattress in the center of the crib and to ensure that not more than half-inch of a gap exists between the crib and the mattress at any point. 

The second guideline is that if you push the mattress completely to one side, there cannot be a gap of more than an inch at any point. If you’re considering an older, hand-me-down crib, we suggest strictly following these guidelines.

Crib Mattress Dimensions:

The crib mattress should always fit snugly inside a standard-sized crib. This helps to ensure that babies cannot climb out of their crib as they grow. Crib mattresses are designed to be slightly smaller than standard crib dimensions. You should ensure that there is no more than a 1-inch gap between the mattress and crib wall. This prevents your baby from any risk of entrapment or suffocation 

To be absolutely sure of the actual mattress size, we suggest you look at product measurements instead of shipping measurements. You shouldn’t purchase mattresses advertised as “mini crib” mattresses which claim to made exclusively for mini cribs as they will be too small.

If you are worried about getting confused with regards to the sizes of crib mattresses, the good news is that you don’t get too many options in this matter.

The size of crib mattresses, along with sizes of cribs, is regulated at the Federal Government level. The two sizes available are the standard crib mattress and the mini crib mattress. These are available separately from the crib.

Standard Crib Mattress Size:

The standard crib mattress are 52 inches long and 27 inches wide. The mattress is typically 5 inches to 6 inches thick and is regulated to not be thicker than 6 inches. The standard crib mattresses are designed to fit snugly inside USA-standard full cribs, which are 52 inches long and 28 inches wide. While testing and installing these mattresses make sure that there shouldn’t be any gaps larger than two fingers wide between the mattress and the crib.

Mini Crib Mattress Size:

Mini or portable cribs are constructed to work well in tight spaces and also are a more budget-friendly option for parents looking for a more portable option. 

The standard mini crib mattress is 38 inches in length and 24 inches wide. The thickness of these mattresses tends to be lower with most around 3 inches to 4 inches high. When it comes to fitting into the crib, we suggest following the same rule just like a standard crib, the gaps between the crib mattress and the sides of the crib should be no more than two fingers wide.

Other Aspects to Consider:

Although you might not get many options to choose from when it comes to the size of a standard crib mattress, you do get options regarding the type of mattress to choose from.

Foam mattresses are often the most popular choice as they are the most reasonably priced crib mattresses available and they are light-weight which makes them easy to handle and clean. Memory foam mattresses are an exception when it comes to the weight department.

Innerspring mattresses are also available and they use coils in their construction. These provide a high level of support. The third type of mattress available are organic mattresses which are made from completely organic products. This means that your baby is not exposed to chemicals or allergens that could potentially be harmful.

When Making a Move to the Crib, Take Care of the Following and You’ll Be Good to Go:

Start Small: Make the switch in stages, this will help the baby get comfortable and accustomed to the crib and the mattress. 

Security: You should make sure your baby’s crib is of the best security standards and meets the latest guidelines. This will not only give your baby a safe sleep but also give you peace of mind during the transition. Follow these simple safety guidelines.

  • There should be no loose or sagging pieces on the crib.
  • Use a firm mattress.
  • Babies should only be placed on their backs to sleep.
  • Don’t cover your baby with a blanket or comforter. Use a sleep sack or warm pajamas.
  • Don’t place stuffed toys in the crib.
  • Bumper pads are unnecessary and potentially dangerous.
  • Careful periodic inspections of the crib for any breakage or damage.

Routine: Make the crib part of your baby’s routine. Also, now’s the time to establish some night-time rituals like bathing, feeding, snuggling, and playing. Your baby will gradually accept that the crib is a safe, secure part of their daily routine.

  • You should sleep with your baby in the same room for the first year.
  • If the crib is too large to fit in your bedroom, set up a place to sleep in the nursery.
  • Have your baby spend some time in the crib every day.
  • Remember that babies need security, familiarity, and routine to feel safe.
  • When it’s time to sleep separately, ease your worries with a baby monitor.


Setting up a safe and secure nursery for your baby is a big exciting part of early parenthood. Your baby will spend the most important formative years in the nursery. Hence, it’s only natural that you will want to pull all the stops to make it just right for your baby. Cribs are a focal point of a child’s nursery and a crib mattress will be where your baby in its early growing years will spend almost 2/3rd of their time.

With all the other things that you are juggling right now in your role as a parent, we hope we were able to help you with our quick guide on crib mattresses, their dimensions, and other crib related issues.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.