Standard Crib Mattress Size: The Best Fit for Baby

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Dreaming of your baby’s crib?

It’s a big purchase, and having it made up and ready for your little one is one of the big milestones in preparing for the day you bring them home.

When you’re buying your baby’s crib, you also need a mattress, and getting one that’s the perfect fit is important for their safety.

So what’s the deal with crib mattress sizes, and how do you get it right?

In this article 📝

Do cribs have different size mattresses?

Yes, there are different crib mattress sizes available, for different sizes of baby and different types of cribs or bassinets.

Baby beds come in all sizes, but the good news is that their mattresses do, too.

Whatever you’ve chosen, you will be able to find the right mattress.

• Standard crib mattress size: These rectangular crib mattresses are the most common, suitable for babies from birth until they’re ready to leave their crib. The standard crib mattress dimensions range from 27.5 inches by 51 ¼ inches to 28 inches by 53 inches.
• Mini crib mattress size: Mini crib mattresses are also rectangular, usually aimed at premature babies or parents with smaller rooms. But, unlike the standard crib mattress size, these aren’t actually regulated, so there’s no specific minimum mini crib mattress size. However, most tend to be around 24 inches by 38 inches.
• Circular, oval, square, or hexagonal crib mattress size: As with mini mattress crib sizes, there’s no hard-and-fast rule for the crib mattress dimensions for different shapes of crib mattresses, as they’re not regulated.

What size is a standard baby bed?

In the US, it’s the law that all cribs must fit what’s known as a standard crib mattress size.

And what size is a standard crib mattress? Well, here’s your standard crib mattress size chart:

• The length of the crib mattress must be between 51 ¼ and 53 inches.
• The width of the crib mattress must be between 27 ½ and 28 inches.
  So as long as you’re not making the crib yourself in your family woodshop, or inheriting an heirloom from before the standard crib mattress sizes were set, it should be a standard size.

This means that a crib mattress that suits it will also be easy to find. Yay!

Are baby cribs a standard size?

Yes, generally speaking, most baby cribs in the US are standard-size cribs ‒ except for mini baby cribs or differently-shaped cribs.

How high should crib mattress be for newborn?

Ideally, baby’s crib mattress should be at least 26 inches from the bottom of the mattress to the top of the crib rail, so baby can’t easily escape.

So when you’re setting up baby’s crib for the first time, get out the measuring tape and make sure the 26 inches are clear.

What size mattress fits in a toddler bed?

Toddler crib mattresses are the same as the standard crib mattress size from 27.5 inches by 51 ¼ inches to 28 inches by 53 inches.

Babies need less give in their sleeping surface, to support them better and to stop them from pushing their hands and feet down the side of the crib mattress and getting stuck, and some parents notice that their toddlers prefer a softer bed.

Lots of cribs also let you remove the sides once your little one gets big enough to climb out on their own.

That’s why some crib mattresses are sold as having a firmer side for young babies in the crib, and a softer side for toddlers.

But as long as the crib mattress is still in good condition, there’s no reason that your future big kid can’t keep using it until they’re ready for a full-size single bed.

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

Yes, the toddler crib mattress size is the same as baby crib mattress dimensions.

What about bassinet and cradle mattress size?

There’s more good news here.

Bassinets, cradles, and mini-cribs are what’s known as ‘non-full size’.

But, although they’re all different shapes, there’s also a law that states that these beds must be sold with a crib mattress that fits them.

So you won’t have any extra shopping stress added to your plate, if you want your peanut to snooze in one of these.

Do crib mattresses make a difference?

Yes, crib mattresses are fundamental to how well baby sleeps and ensuring that they’re sleeping safely.

Firmer crib mattresses can make the difference between safe sleeping and unsafe sleeping.

A softer crib mattress may not provide the necessary support to baby’s frame and may put them at risk of suffocation of SIDS (sudden infant death syndrome).

You might think that sleeping on a firm mattress would be uncomfortable for baby, but that’s not the case ‒ they don’t have the same sleep habits as adults yet.

How do you know that the mattress fits?

If you can put more than two fingers between the mattress and the edge of the crib, it’s too small.

Although it feels like a very small gap, babies wriggle a lot when they sleep, and if there’s even a chance they could get stuck, you should swap the mattress for one that’s a better fit.

How tight should a crib mattress fit?

Crib mattresses should fit snugly into the crib ‒ not so tight as to cause any features, like a drop-side, not to work, but a rule of thumb (or finger) is to put two fingers between the mattress and the edge of the crib.

If there’s room, it’s too small, and you need to get a bigger crib mattress size.

How do I choose a crib mattress?

If you have a standard crib, just measure the inside, and buy a mattress that matches or is very slightly smaller than those dimensions ‒ a standard crib mattress should do the job.

And if your baby is going to be catching their Zs in something smaller, the crib mattress will already be included when you buy it.

Other standard crib mattress size FAQs

Choosing the right crib and crib mattress size for your little one can be overwhelming, so let us ease your mind by answering your burning questions.

How many mattresses do you need for a crib?

Most of our Peanut mamas only have one crib mattress per crib.

Worried about accidents? Invest in a couple of washable crib mattress covers to catch any leakages.

What do you put under crib mattress?

You don’t need to put anything under baby’s crib mattress ‒ there should be 26 inches between the crib mattress and the top of the crib, so baby can’t get out when they can stand.

All you need for baby’s crib is a crib mattress, fitted sheet, and crib covers, if you want.

Is it OK to reuse a crib mattress?

Yes, you can reuse a crib mattress if you’re buying one secondhand or using one from your older baby.

However, you must make sure that it appropriately fits your crib and is still firm ‒ some baby crib mattresses can get softer over time.

How often should you replace a crib mattress?

It depends on the crib mattress manufacturer ‒ some are designed to be used for up to 5 years, some less.

If you’re not sure, it’s best to make sure the crib mattress is still firm and hasn’t sagged before you put it in baby’s crib.

Should a baby mattress be firm or soft?

Baby crib mattresses should be firm.

They might seem like they’d be uncomfortable to sleep on, but a firm crib mattress is fundamental for baby to sleep safely.

How do I know if my baby mattress is firm enough?

It’s all in the spring-back ‒ push on the baby crib mattress in the center, at the corner, and at the edges.

It should spring back straightaway without staying pushed in.

Are foam mattresses OK for babies?

Yes, but as long as the foam mattress is specially designed for babies.

Most adult foam mattresses sink to curve around your frame, but that’s not what we want when looking at baby crib mattresses.

Make sure your foam crib mattress is firm enough by doing the spring-back test ‒ push on the crib mattress at different points, and it should spring back immediately.

As long as baby doesn’t sink into the memory foam crib mattress, it should be safe.

Does a crib mattress need a fitted sheet?

Yes ‒ they can help make a firm mattress feel a little softer (in texture) to baby’s touch and can help their skin from being irritated.

Crib sheets are also much easier to clean than crib mattresses.

Is a 30-year-old crib mattress safe?

Probably not ‒ as with adult mattresses, crib mattresses can lose their spring over time.

Baby’s crib mattress should be very firm.

Older mattresses may also harbor some germs, too, so sometimes, it can be best to buy something a little newer.

Can plastic crib mattresses get bed bugs?

Not often, no ‒ crib mattresses covered with plastic (which is great as a waterproof solution) then a fitted sheet tend to stop bed bugs from making baby’s crib their home.

How thick should my baby's mattress be?

As for thickness, crib mattresses are usually between 4 and 6 inches thick, depending on what they’re made from.

Thicker isn’t necessarily better.

Your baby will get the safest sleep on a crib mattress that’s firm, supportive, and fits the crib frame, however thick it is.

Does a standard crib mattress fit an IKEA crib?

Yes, absolutely.

The standard crib dimensions at IKEA in the US are 52 by 27 ½ inches.

IKEA crib mattresses have exactly the same dimensions, but any other standard crib mattress should also fit.

And, just as we said above, the cradle that they stock will come with a fitted sleeping pad.

That’s all there is to know about standard crib mattress sizes and how to get the best fit for your baby’s crib mattress.

Got any other questions about crib mattresses or getting the right set-up so baby can sleep soundly and safely? Join Peanut and ask our community of veteran mamas!

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