Knowing how big a crib mattress is can help you to make choices for your baby’s sleep environment. The standardization of baby crib mattress sizes has prevented dangerous gaps in cribs and costly frustrations when the mattress wouldn’t be right for the crib you’ve purchased. The key is to know what are the most common types of cribs and to purchase a mattress in the recommended size range for the one you got. 

Different Crib Types

Standard Crib

This standard crib will seem large for a newborn baby, but they quickly grow. A mattress this large gives you room to use it for a couple of years. It is also the size for most toddler beds and convertible cribs, so using a traditional crib mattress from the beginning allows you to use the same mattress later in the child’s life. You can lower the height of your baby’s crib or remove a side when the child becomes a toddler if the model you bought allows you to do so. 

Mini Crib

Mini cribs are meant to fit in smaller spaces and be more portable, which means it will only fit babies and toddlers who are on the younger end. These cribs are ideal for tighter rooms, when a baby is rooming with a parent or sibling, or when traveling. Grandparents might even get a mini crib or portable crib on wheels, because the mini crib dimensions fit in small rooms or can be folded up or rolled away. 

Shaped Cribs

While all standard rectangular cribs should conform to the two sizes above, if your crib is designed with a curve in one or more sides, it will need an unique-shaped mattress. You’ll need to either purchase the proprietary mattress intended to go with the crib, or you’ll want to take careful measurements to look for a shaped crib mattress that will fit precisely to the shape of the crib.

How To Choose The Right Mattress Size For Your Crib 

Crib mattresses should conform to specific dimensions, including the mini crib dimensions or the standard crib mattress size. Because small hands can become pinched or stuck between a mattress and the crib, the mattress is intended to fit very snuggly into the crib to provide the safest possible sleep environment. Choose a firm crib mattress that fits the interior dimensions of your crib as closely as possible. 

Standard Crib

To make things simple for families and to ensure safety in the crib, the standard crib will snuggly fit a mattress that is 28” by 52,” and almost all mattresses you encounter that are called crib mattresses or toddler bed mattresses will be of this size.

Mini Crib

For small or portable cribs, you’ll opt for the recommended dimensions of 38” by 24”. This is a standard size for mini cribs, and many mattress makers have this size. Because mini cribs sometimes also have slightly lower sides than a standard crib, you may opt for a thinner mattress as well; to make it harder for an older baby to pull themselves up or climb out.

Shaped Cribs

Choosing a crib mattress sold with the shaped crib and its custom dimensions is the best way to handle using a shaped crib. If you don’t like the materials or quality on the included or suggested shaped crib mattress, take those dimensions and see online whether other crib mattress manufacturers create an equivalent product.

Other Considerations When Deciding On A Crib Mattress 


The American Association of Pediatricians advocates that the surface a baby sleeps on should be firm since soft materials can conform around the face rather than leaving open airflow. Most crib mattress manufacturers know this, but if you encounter a soft crib mattress, steer clear until the child is older and can choose a softer sleep surface. 


For many, choosing an affordable, lower-end crib mattress is a good choice since children sleep on crib mattresses for such a short time. However, if you intend to have multiple children, investing in one high-quality crib mattress that can be well-protected and used for many years may also be a smart option.


As mentioned above, most crib mattresses are firm and won’t undergo enough wear and tear in one child’s use to need replacing. However, if you intend to pass along a crib mattress as a hand-me-down or use it with other children, look for long-term reviews and see what parents of multiple children say about its durability.


Most crib mattresses are 4 to 6 inches thick, so anything substantially thinner or thicker than that should not be considered. It may be too thin to be comfortable for an older baby or too thick to maintain plenty of crib height to keep the baby safe.


Some mattress brands boast being “100% breathable,” so that babies who sleep face-down on them can still breathe through them. Most babies will adjust to maintain their airway, but if you have concerns about your child sleeping face down after the standard early months of sleeping on their back, you might consider switching to a high-breathability mattress.

Final Thoughts 

Choosing the right crib mattress size for you should focus on making sure it fits the crib dimensions you’ve chosen and its firmness. Your preferences for materials, durability, and breathability can also impact your choice, but buy either a standard size or mini size crib mattress unless you have a shaped crib requiring a custom size mattress.


How big is a standard crib mattress?

A standard crib mattress will fit into a fairly strict size measurement since it needs to fit a standard crib snuggly. The standard crib mattress is 52 inches by 28 inches.

Is the baby crib mattress size the same size as a toddler mattress?

Crib mattresses and toddler mattresses are the same size, offering the opportunity to use it as your baby grows.

What size mattress do I need for a convertible crib?

Unless the convertible crib is labeled as a mini-crib, it should use a standard sized crib mattress.