Crib Mattress Size | Baby Journey

Everything You Need to Know About Choosing the Right Crib Mattress Size

When it comes to crib mattresses, size is an important factor that is often overlooked. Yet, it plays a major role in keeping your baby comfortable and safe.

Still, there is no reason to be hard on yourself. There are a lot of details that go into finding the right crib mattress size. Couple that with all the crib mattress brands in the market and you may, understandably, start feeling out of your depth.

So, how about we take that load off your shoulders?

In this article, we discuss everything you need to know about choosing the right crib mattress size and how to navigate the entire process.

Why is Crib Mattress Size Important?

The crib mattress size determines whether it will fit in the crib. If the mattress is bigger than any of the crib’s dimensions, it will not fit unless you force it in.

That should be your first indicator that it is not the right crib mattress for your needs.

Properly Fitting Crib Mattress | Crib Mattress Size | Baby Journey
A properly fitting crib mattress is comfy and safe. Source: Pinterest

On the other hand, it could be that the crib mattress is small and there are gaps between it and the sides of the crib. This is actually a common problem that most parents ignore or try to make up for by filling the gaps with baby blankets or pillows.

While well-intended, using ‘gap fillers’ would likely put your baby at risk for suffocation. If they roll over and faceplant on the blanket/pillow, it can block their airways. Further, the mattress and the gap-fillers can create an uneven sleeping surface which pediatric medical experts associate with SIDs/SUIDs.

Leaving gaps between a small mattress and the sides of the crib is also quite risky. Your baby’s arms or legs can get stuck in such gaps which could result in injury.

How to Tell That a Crib Mattress is a Proper Fit

As a rule of thumb, there should not be more than one inch of space between the crib mattress and the sides of the crib. Safety experts further recommend that a crib mattress should not be thicker than 6 inches.

For the avoidance of doubt and error, it is best to rely on precise measurements. Additionally, take note of the measurements indicated by the crib manufacturer. They are legally required to be precise and so even if you choose to take your own measurements, you will have something to compare them against.

Crib Mattress | Crib Mattress Size | Baby Journey
The right size crib mattress fits into the crib with ease. Source: Pinterest

Are All Crib Mattresses the Same Size?

The brief answer to this is: no, they are not. For a better understanding, let’s back up a little and discuss crib sizes before we circle back to crib mattress sizes.

Understanding Crib Sizes

There are 2 well-established crib sizes used by the majority of manufacturers:

  • Mini crib size
  • Standard crib size

A mini crib is ideal for infants and is made in a smaller size than a standard-size crib. It has a typical crib length of 38 inches and a width of 24 inches (L 38″ × W 24″). In contrast, a standard crib is larger and its average dimensions are 52 inches in length and 28 inches in width (L 52″ × W 28″).

However, because manufacturing can not be fully standardized, these average crib sizes are allowed as a variance of between 3/8 to 5/8 of an inch between brands. This is why it is always important to specifically take note of the dimensions of your crib as not all mini or standard cribs are identical.

Additionally, if you prefer shaped/custom baby cribs, keep in mind that they come with unique dimensions. It is best to find out what those dimensions are and whether you can find a matching crib mattress for them. Better still, aim for a custom crib manufacturer that offers custom mattresses for their products in line with Consumer Protection Safety Commission guidelines.

Mini Crib and Full Size Crib | Crib Mattress Size | Baby Journey
Mini cribs and full size cribs require different mattresses. Source:

Matching Crib Size and Crib Mattress Size

Given that mini cribs and standard cribs have regulated sizes, mattresses for these types of cribs are also standardized.

The average mini crib mattress size is 38 inches by 24 inches (L 38″ × W 24″). Nonetheless, you will encounter numerous brands that offer mini crib mattresses with variations of these measurements. The upside of this is that it raises the odds of you finding a perfect fit even if your mini crib dimensions are a few microinches larger or a bit smaller than usual.

Standard mattress size dimensions are more closely regulated than mini crib mattress sizes. The United States Consumer Product Safety Act stipulates that the minimum dimensions of a standard crib mattress should be 27 ¼ inches by 51 ¼ inches. [1] That said, these dimensions can vary by a fraction or so to accommodate different design and manufacturing variations.

On mattress height, all crib mattresses should not exceed 6 inches. This measurement is predicated on typical crib height. If the crib mattress is any thicker, it means the baby would be closer to the top of the railing of the crib and this could eventually present a risk of them falling over.

Tips on Choosing the Right Crib Mattress

Size is a crucial consideration when choosing a crib mattress. However, it is not the end all be all. It is essential that you also consider other mattress features such as:


Whenever weight is exerted on a mattress, it is pressed downwards to a certain degree. A firm mattress will only compress slightly while a soft one will compress significantly under the pressure of weight.

So, what does firmness have to do with baby crib mattresses?

The American Academy of Pediatrics recommends firm crib mattresses to prevent SIDS and SUIDS. [2] This is because infants do not have well-developed skeletal muscles or motor skills. If a crib mattress tends to sink in, it can obstruct their breathing and they would not be able to move themselves to a safer position.

A firm mattress that provides a flat, even sleeping surface significantly reduces the risk of mattress suffocation and subsequent SIDS/SUIDS.


As your baby’s motor skills develop, they begin to roll over in their sleep even if the crib mattress is flat, even, and firm. When they lie on their belly their airways can get obstructed by the mattress and cause suffocation.

A breathable crib mattress, such as the Newton Wovenaire mattress, allows for air to flow through the structure of the mattress. Both the materials used to make such mattresses and their mattress covers are porous. In other words, even if your baby faceplanted in their sleep, they would still be able to breathe just fine.

Breathable crib mattresses often cost a bit more than ordinary mattresses. Nonetheless, the peace of mind they bring is arguably worth it. Moreover, if you are worried about their ‘porosity’ and baby messes, you will be happy to know that there are breathable waterproof options. The Newton Waterproof mattress, for example, will not only prevent liquids from leaking through but you can also clean all its parts whenever you need to.

Breathable Air Mattress | Crib Mattress Size | Baby Journey
The structure of breathable air mattresses allows free air flow. Source: Pinterest


When buying baby items, I think of durability in two ways:

  • Is the quality good enough to last
  • Can my baby transition through different stages while using the item

In this case, aim for a quality crib mattress that :

  • Will not lose its firmness
  • Is easy to clean without the mattress becoming damaged
  • Has protective features like a waterproof or easy to clean mattress cover

All these factors will make it easy to keep the baby mattress in good condition and get maximum value out of it.

You are also more likely to get long-term service from a standard crib mattress than a mini crib mattress. Babies tend to outgrow mini cribs quickly but a standard size crib and mattress can serve you until the toddler years.

Important Baby Crib Safety Tips

It is estimated that about 3000 babies die in the USA due to SIDS/SUIDS every year. [3] Research further indicates that these deaths predominantly occur in the babies’ cribs or general sleeping areas. This is an alarming statistic that, unfortunately, can manifest in any home.

The silver lining to all of this research is that health authority bodies like the CDC and the American Academy of Pediatrics, have found ways through which SIDS/SUIDS can be prevented. Here are some of the crib safety tips that they recommend.

Keep Soft Toys and Bedding Away

Understandably, you would like to make your baby’s sleeping area as cozy as possible. Most parents do this by placing soft plush blankets and their baby’s favorite toy in the crib. This is not a safe idea.

Soft toys and bedding are suffocation hazards. If your baby turns their face into such items, they would not be able to breathe and the lack of air can result in brain damage or death.

Use fitted crib sheets and keep all clutter away from the crib. It may also be safer to consider getting breathable crib sheets.

Place Your Baby on Their Back at Bedtime

Infants are not able to properly lift their necks or turn themselves over. Subsequently, if you place them on their tummy at bedtime they will be stuck in that position even when they are not breathing right.

In contrast, placing your baby on their back keeps their airways open and poses no risk of suffocation.

Choose Bedding Carefully

As we have discussed, fitted crib sheets that are breathable are a safe choice of bedding. However, there are other bedding decisions to make.

On fabric, aim for hypoallergenic fabric to avoid allergic reactions such as a blocked nose, sneezing, or adverse skin reactions. A breathable mattress cover could also be helpful as it would protect the mattress from damage while keeping your baby safe and comfortable.

Well-fitted Sheets | Crib Mattress Size | Baby Journey
Well-fitted crib sheets are safer for babies. Source: Pinterest

Ensure Proper Flow of Air in and Around the Crib

Heaters in rooms with poor ventilation and carbon monoxide are all hazards that could cause SIDS/SUIDS. Make an effort to ensure that your baby’s sleeping area is well ventilated and that they are protected from any fumes. It is best to avoid the use of room heaters when you are not in the nursery.


When you know what to look out for, choosing the right crib mattress size is a lot easier. All you have to do is budget, compare options, and find crib mattress options that meet your needs.

Newton crib mattresses are currently the apple of my eye. With their 100% breathability, you would not have to check your baby’s pulse every few minutes during their nap like I did with mine. It is also an absolute plus in my book that they are fully cleanable.

I look forward to reading your comments about what your mattress hunting experience has been like and what you learned from it.

Crib Mattress Size | Baby Journey

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