Crib Mattress Size – The Complete Guide

crib mattress size

Crib Mattress Size – The Complete Guide

You must be very excited to have a new little one on the way.  There are a lot of things you will need.  First and foremost is a safe place for baby to sleep.  Your little one will be doing a lot of sleeping.  In fact, your baby will spend 70% of their first year in a crib. 

Once you figure out the best crib for your baby, you will need to choose a crib mattress.  Since your baby will spend so much time in their crib, you want to make sure to get a crib mattress that is safe and fits correctly in the crib.

The professionals at SafeSleep® are here to help you navigate the different types of cribs and their corresponding crib mattress size.  This information will help you make an informed decision on what crib and mattress is best for their little one.

Two Basic Crib Sizes

There are two basic crib sizes.  One is considered a standard size crib.  The other is referred to as a mini crib or nanny crib.

Standard Crib

The standard size crib must meet strict CPSC size guidelines to be called a “standard size crib.  These standards are designed to prevent head entrapment and suffocation between the mattress and crib sides.  The CPSC outlines very specific tolerances for the interior dimensions of a standard size cribs.  This ensures a “standard size” crib will fit and be safe.

A standard size crib mattress is also referred to as a full-size crib.

According to the CPSC, the interior dimensions of a standard or full-size crib must be 28” inches plus or minus 5/8” in width.  The length must be 52 3/8” plus or minus 5/8”.

A standard-sized crib is the typical go-to for most parents. The reason is they can be used for up to 3 years. Additionally, many full-size cribs convert to toddler beds.  Once your baby discovers how to climb out of their crib, you won’t need to buy a new bed. This feature makes it possible for your child to enjoy their crib until about 5 years old.

Mini Crib

A mini crib is also known as a nanny crib.  Often you will see this type of crib used in childcare centers.  Since they are often used in childcare centers, most mini cribs have casters on them.  This feature makes it possible to evacuate babies should a fire or other emergency arise in a childcare center.

Most mini cribs have an interior dimension that is normally 23 3/8″ wide.  The length is 37 3/8″.  Unlike a standard size crib, the size of a mini crib is not regulated.  Consequently, you will want to make sure you have the interior dimension when shopping for your min crib mattress.

A mini crib is a great option for a small room.  It’s also a great option for grandpa and grandma’s house.  The fact it is on casters makes it easy to move from room to room.  Just be sure the wheels are locked, and the crib is securely in place when you’re not moving it.

As far as price goes, both a standard size crib and a mini crib can range in price from under $100 on up to over $1,000. 

Be sure your crib has been certified and meets all the CPSC regulations.  Do not purchase or use a crib that is over 10 years old.  Also, make sure there are no broken or modified parts.  Older cribs did not have to pass the stricter safety guidelines cribs do now. 

Shaped Cribs

Most cribs are rectangular in shape.  However, you will see some unique variations in shapes of some more expensive cribs.  For the most part, these round or oval shaped cribs will come equipped with a mattress.  Just remember, it will be difficult to find the shaped bedding if you don’t like the crib manufacture’s selections.

Choosing Your Crib Mattress

Standard Size

Now that you have found the prefect crib, it is time to find the mattress. 

There are many things to consider when buying your crib mattress which we will discuss.  But first, you want to make sure you choose the correct size mattress for your crib.  If you are going with a standard full-size crib, you want to look for a “standard” size crib mattress. 

As we mention, the size of a standard crib mattress is regulated. However, there is some tolerance within the regulated size of a crib.  As stated, a standard crib can be ⅝ of an inch larger or smaller than the regulated 28 by 52 ⅜ rectangle.

Consequently, a mattress used in a full-size crib must be at least 27 1/4 inches by 51 1/4 inches. Obviously, a crib mattress should not exceed 28” wide.  And it should not be any longer than 52 3/8 inches in length. 


what size is a crib mattress


Additional things you want to check for regarding the size of the crib mattress, is fit and height.  The mattress should be at least 4″ thick.  It should not be any thicker than 6”.  This is to protect a baby who is standing up from fall out of the crib.

The other thing you want to check for is the fit.  There should not be a gap larger than 1” between the sides of the crib and the mattress.  An easy way to test is to place two fingers down the side the inside side of the crib and the outside of the mattress.  

As a rule, when the mattress is inside the crib, you should not be able to fit more than two fingers between it and the side of the crib.  If a gap larger than 1” exists, the mattress is not safe for your baby. Be sure to check the fit of our crib mattress inside the crib before letting your baby sleep in it.


Unfortunately, the government does not regulate the size of mini crib mattresses.  The typical size of a mini mattress is 24 inches wide by 38 inches long.  If you are going with the mini crib option, make sure you measure the interior of your crib prior to purchasing your mattress.

You want your mattress to fit snug but not too snug.  You also want to follow the same rules when checking for gaps in the size of your mini mattress.  Mini crib mattresses are typically not as thick as a standard size mattress.  But check to make sure it is not over 6” thick.

Additional Things to Look for When Choosing a Crib Mattress

The medical professionals at SafeSleep® want to share other safety features you should look for when deciding on a crib mattress for your little one.  There are numerous types of crib mattresses.  Some are safer than others. 


Your baby’s crib mattress should be firm.  This does not mean it needs to be rock hard.  Most parents believe the firmness recommendation is to ensure the proper growth and development of a baby’s bones.  This is not the case. 

Infants have soft, malleable bones.  In fact, their skull is like puzzle pieces that flex so they can get out of the birth canal.  Over time, their skull fuses together and hardens.  Also, a lot of what will eventually be harder bones and cartilage, start out rather soft in infants. 

We see the havoc a hard surface can play on an infant’s skull.  Plagiocephaly, also known as flat head syndrome, is on the rise.  This condition in infants started appearing in the mid 1990’s with the onset of the back-to-sleep campaign. 

This condition is attributed to infants sleeping on their back with positional pressure from firm objects on their soft, malleable skulls.  I believe plagiocephaly is convincing enough to realize that a hard, firm crib mattress or sleep surface is not the ideal condition for a baby’s bone and skull development.  

However, a firm crib mattress is known to prevent suffocation risk should your baby end up face down.  Fortunately, there are now crib mattresses that have no fiber fill that are scientifically proven safer than traditional and even breathable crib mattresses.  These crib mattresses allow a baby to breathe normally through their mattress should they end up face down.

Before the availability of breathe-through crib mattresses, a firm crib mattress was recommended to help prevent suffocation risk.  The belief is that a harder, flat surface avoids face compression.

These are just a few things to be aware of when deciding on a crib mattress.  You can check out our in-depth analysis of crib mattress to find out the different types, and designs by reading Baby Mattress for Crib – What to Look For.

Breathable vs. Breathe-Through

The SafeSleep® Breathe-Through Crib Mattress is a mattress that contains no fiberfill or core of any type. The SafeSleep® is a two-part mattress system consisting of an open frame with side openings.  Additionally, there is an open-celled, air permeable top (topper) surface that allows passive airflow.

The topper is suspended over the hollow base using a unique locking bar system.  This feature gives the mattress it’s firmness.

Oxygen rich air travels in and out of the base and up and down through the open celled topper.  This design eliminates both suffocation and the risk of rebreathing CO2.  This is an important advantage to a 100% breathe-through crib mattress.

Currently, there are no standard for “breathble.”  Not all breathable crib mattresses are created the same.  In fact, some crib mattresses claiming to be breathable are actually more dangerous because they retain high levels of CO2.  

Learn more about breathable crib mattress designs and their effectiveness by reading Breathable Crib Mattress – Breathable Crib Mattress – Medical and Safe Sleep Experts Explain

Other Advantages of the SafeSleep®

Other safety advantages of the SafeSleep® include temperature regulation.  Your baby sleeps better since they will not be too hot or too cold. 

The SafeSleep® is firm.  However, it does not have the positional pressure of a traditional mattress.  Instead, it gently cradling cradles your baby’s head and body the way nature intended.

The SafeSleep® is completely washable.  The topper is easily removed for machine washing and the base can be wiped clean while in the crib.  No bathtub or shower is required.  And no sheets or other bedding are used.

size of crib mattresses


The SafeSleep® was designed by a leading pediatrician and a safe sleep expert.  It is the #1 pediatrician recommended crib mattress.  As you prepare for the arrival of your little one, keep in mind your baby will spend 70% of their first year in their crib.  So be sure to make the choice pediatricians use for their babies. 

There is a significant difference between breathable and breathe-through crib mattresses.   SafeSleep® is tested showing 100% oxygen rich air when baby is breathing through it.  It is also 100% washable and recyclable.  

Find out more about Organic Crib Mattress and the chemicals you should avoid.

Find out more why the SafeSleep® is the best crib mattress based on scientific testing and studies by reading Best Crib Mattress – The Science Speaks.


Your baby will spend a lot of time in their crib their first year.  Make sure the crib you choose is safe and meets all CPSC regulations.  Be sure not to use a crib that is older than 10 years.  

Crib mattresses come in many varieties.  Your biggest concern with your crib mattress should be safety.  After all, it is the one place your baby will spend a lot of time unsupervised.  SafeSleep® is the number one choice of pediatricians and safe sleep policy makers.  It is the only crib mattress that tests for 100% oxygen rich air while a baby is sleeping through it.  

Learn more crib mattress facts and information based on scientific studies and recommendations from key child safety advocates.

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