So here’s the thing — bassinet mattresses seem like they’d be a standard size, right? But they’re really not. I figured they’d all just be mini versions of crib mattresses, but turns out the dimensions of a bassinet mattress depend way more on the brand and model than I expected.

You’ll usually see something around 30 to 33 inches long and 15 to 18 inches wide. That’s pretty typical — kind of the “standard bassinet mattress size” — but even within that range, small differences matter. Like, a half-inch gap on each side might not sound like much… but when you’re putting your newborn down at 2 a.m. and worrying if they’ll roll into a space too big, it’s not a detail you want to ignore.

If you’re already deep in mattress comparisons, this might help too: how to choose the best crib mattress — it’s crib-focused, but a lot of the logic applies to bassinets too.

And if you’re jumping ahead and thinking long-term, you can peek at the best crib mattresses while you’re at it — for whenever you’re ready to make that move.

Let’s break it down a bit more.

Understanding Bassinet Mattress Dimensions

Choosing the right size isn’t just a fit issue — it’s a safety one. Too small, and you’ve got gaps. Too tight, and it bunches up or curls. Either way… not good.

Standard Dimensions for Bassinet Mattresses

Honestly, this is the part i wish was more straightforward. But here’s what “standard” typically looks like:

• 30 x 15 inches — probably the most common, especially for basic oval or rectangular bassinets
• 31 x 16 inches — still fits in the standard category, just a bit roomier
• 32 x 17 inches — closer to crib mini-mattress territory, but still technically “bassinet”
• 33 x 18 inches — rare, but you’ll see it in some higher-end models

Per Newton Baby’s bassinet guide, those are the most frequent measurements, and they stress how important it is to match your mattress exactly to avoid suffocation hazards — no more than a finger or two of wiggle room around the edges.

If you’re curious how that compares with crib sizes, this might help: what are the dimensions of a crib mattress — just to get a feel for the size jump.

Variations by Brand and Model

This is where things get fussy. Some brands use oddball sizes that don’t match anything else. Helpful, right?

The 4moms mamaRoo mattress, for example, is 29 by 17 — which sounds close enough… until you try to swap in another mattress or find a fitted sheet that actually hugs the corners.

It’s also why crib mattresses aren’t universal (if you’re wondering, here’s a good breakdown on that whole crib mattress compatibility thing).

Basically, always measure first. And if you’re buying a third-party mattress, double-check compatibility — some brands are really picky. If you’re leaning into crib research already, these top-rated mattresses might give you a head start for later.

How to Measure a Bassinet Mattress

Not sure what size your bassinet needs — or if your current mattress fits right? Here’s the simplest way to check:

1. Clear the bassinet — take out any mattress, pads, or liners.
2. Use a soft measuring tape — like the sewing kind, not a rigid ruler.
3. Measure the interior — length and width, from the inside wall to the opposite wall.
4. Check the depth — not always necessary, but helpful if you’re replacing the mattress.
5. Do the finger test — slide two fingers between the mattress and the side. If more than that fits, it’s too loose.

Safety and Fit Considerations for Bassinet Mattresses

Importance of Snug Fit

So here’s the deal—fit really matters. Like, not “oh that’s a little loose but fine” matters… it needs to be snug. You shouldn’t be able to wedge more than two fingers between the mattress and the bassinet frame. If there’s a gap, that’s a risk—babies can roll into those spaces and get stuck. And yeah, it sounds a little dramatic, but it’s not rare. Even just a half-inch of extra space can be a problem.

The Plunket safe sleep guidelines back this up—they specifically say the mattress should sit flush against all sides of the bassinet. No gaps. No sliding around. Just a firm, tight fit. If your bassinet mattress isn’t fitting quite right, it’s not one of those “eh, close enough” things. You really do need to swap it for something that matches the exact dimensions. It’s the kind of small detail that can make a big difference in safety.

If you want a broader look at keeping baby safe overnight, this breakdown on how to keep baby safe in the crib covers the bigger picture.

Recommended Thickness for Bassinet Mattresses

Here’s something that caught me off guard at first — bassinet mattresses are super thin. Like, one to one-and-a-half inches thick. Honestly, they don’t look comfortable. But there’s a reason for it.

According to Halo Sleep’s safety guide, that thinness is intentional. A firm, not-too-thick mattress helps reduce the risk of suffocation because it keeps your baby’s face from sinking in. It’s the same reason crib mattresses feel hard, by the way. What seems stiff to us actually helps babies sleep more safely.

So if you’re wondering, “how thick should a bassinet mattress be?” — the answer is just thick enough to be firm, supportive, and safe. Usually between 1″ and 1.5″, and not much more.

Here’s a quick link if you’re curious about why crib mattresses feel so firm.

Safety Standards and Certifications

Certifications aren’t just sticker fluff — they’re the behind-the-scenes checks that tell you a mattress has passed actual safety tests. If you’re wondering what to look for, here’s a quick breakdown:

• CPSC bassinet mattress guidelines: These cover basic safety standards like flammability, fit, and stability. Any product sold in the U.S. should meet these.
• JPMA Certification: This one’s a little more thorough. If a mattress is JPMA certified, that means it’s been tested to meet ASTM standards, including things like proper sizing, chemical safety, and structural integrity. It’s basically a vote of confidence that the thing won’t fall apart or fail you.

The JPMA certification standards page walks through what those certifications cover — and honestly, it’s kind of reassuring when a product’s gone through that process. Especially when you’re up at 2 a.m. second-guessing everything.

If you want to go a little deeper into safety, there’s also a broader look at baby crib safety standards.

H2: Types of Bassinet Mattresses

Oval vs. Rectangular Bassinet Mattresses

Shape isn’t just about aesthetics — it affects everything from fit to bedding options to whether you can even find a replacement down the line. Most bassinet mattresses fall into two camps: oval or rectangular.

Newton Baby points this out in their bassinet shape guide — the shape makes a difference when you’re dealing with tight fits. So if you’re using oval, double-check your measurements and don’t assume all sheets or pads will stretch to match.

If you’re not quite ready for the bassinet stage to end, some best crib mattresses might help you think ahead.

Breathable and Hypoallergenic Options

There’s a lot of buzz around breathable bassinet mattresses, especially from nervous parents hoping to reduce SIDS risks. Totally understandable — but here’s the honest take.

According to ParentData, there’s no solid evidence that breathable mattresses actually lower SIDS risk. What does matter is firmness, fit, and keeping the sleep space clear. So, if a breathable design helps you feel more at ease, go for it — just don’t expect it to replace other safe sleep practices.

Hypoallergenic bassinet mattresses can be a good option too, especially if there’s family history of allergies or eczema. Some models use organic cotton covers or avoid common irritants (no vinyl, no polyurethane foam). That said, unless your baby has shown signs of skin sensitivity, it’s more of a “nice-to-have” than a must.

For a better understanding of breathability, here’s a deeper dive: are crib mattresses breathable?

Still, if you’re browsing with all this in mind, this list of best crib mattresses covers several that overlap with bassinet-safe features.

Replacement and Custom Mattresses

This part trips people up a lot — like, you realize the original mattress is too thin, worn out, or just gross… and then? Finding a replacement bassinet mattress pad that fits perfectly can feel like hunting for socks in the dark.

The trick is to go back to your exact dimensions. No rounding. No “eh, close enough.” Take a flexible tape measure, get that width and length right down to the quarter-inch, and start from there.

Some bassinets — like the 4moms mamaRoo — list their dimensions clearly (17” x 29” in that case), and even sell their replacement waterproof covers based on those specs. So if you’re using one of those, definitely check for accessories made specifically for that model.

Custom options are out there too, especially on Etsy or specialty baby sites. Just make sure the materials meet safety standards, and avoid super plush or thick designs. If you’re ever unsure whether it’s time to replace — or wondering if you can reuse something — here’s a guide on whether crib mattresses can be reused.

And if you’re switching to a crib soon anyway, now might be the time to look into best crib mattresses that’ll last a bit longer. Just something to keep in mind while you’re measuring things in your socks at 11 p.m.

Choosing the Right Bassinet Mattress

Top Picks for Bassinet Mattresses

Here’s the thing — you don’t need the best mattress. You just need one that’s firm, fits well, and works with your bassinet. Still, if you want a few solid options to compare, here’s a quick look:

(If you’re also looking into cribs down the line, this might help: what are the best crib mattresses.)

Bedding and Sheet Compatibility

A bassinet mattress is only as safe as the sheet that goes over it — which sounds dramatic, but… it’s true. Loose bedding is one of those little things that can quietly become a big safety risk.

Here’s what usually works:

• Standard bassinet sheets: Around 33” x 15”, like these Burt’s Bees options. They’re snug and soft.
• Waterproof protectors: Also need to fit flush. No bunching. No weird corners poking up.
• If your bassinet is an odd shape (oval or custom), measure it yourself — and check the sheet specs twice.

More on that here if you’re sorting through crib sheets too: what are the dimensions of a crib sheet

And if you’re still building your setup: essential furniture for nursery

Tips for Selecting a Safe and Comfortable Mattress

Not sure where to start? This quick checklist might help:

• ✅ Fits your bassinet without gaps (seriously — gaps = risk)
• ✅ Thickness stays in the 1–1.5″ range (anything softer or deeper can be unsafe)
• ✅ Firm to the touch (if it feels cushy, it’s probably too soft)
• ✅ JPMA certified, or at least follows CPSC guidelines
• ✅ Comes with (or works with) a tightly fitted sheet — Halo makes a point about this, and it’s worth listening to.

Need more help thinking through mattress traits? Try this guide too: how to choose the best crib mattress

Key Takeaways

• Snug fit is non-negotiable. No gaps. No shifting.
• Firm and thin is safer than soft and plush — even if it looks cozier.
• Most bassinet mattresses fall in the 30–33” x 15–18” range — but measure yours before buying replacements or sheets.
• Watch out for “extras” that don’t actually improve safety — like overly padded toppers or loosely fitted protectors.

For the bigger picture, here’s our ultimate crib buying guide. And if you’re still outfitting the nursery, the essential furniture for nursery post can help you sort through the noise.

References

• Newton Baby bassinet guide
• Plunket safe sleep guidelines
• Halo Sleep bassinet safety
• JPMA certification standards
• ParentData breathable mattresses
• CPSC crib mattress regulations
• Burt’s Bees bassinet sheets

Related Posts

• how to choose the best crib mattress
• what are the dimensions of a crib mattress
• are crib mattresses breathable
• baby crib safety standards
• how to keep baby safe in the crib
• what are the best crib mattresses
• ultimate crib buying guide

FAQs

What is the standard bassinet mattress size?

Honestly, there’s no true “standard,” but most bassinet mattresses fall in this general range:

Some brands follow their own sizing — so always check the product listing or measure your bassinet to be sure. A snug fit is key here. No gaps along the sides. Newton Baby puts it simply: if you can fit more than two fingers between the mattress and the bassinet frame, it’s too small. (Newton Baby bassinet guide)

One parent trick? Grab a soft tape measure and write the dimensions on your phone before shopping — easy to forget when you’re juggling a million tabs. If you’re comparing with crib sizes too, here’s a breakdown: what are the dimensions of a crib mattress. Or browse some best crib mattresses if you’re planning ahead.

How thick does a bassinet mattress need to be?

Most are just 1–1.5 inches thick — and that’s on purpose. Thinner mattresses are firmer, which reduces the risk of suffocation. Plunket’s safe sleep guidance says no more than 40 mm thick (which is about 1.57 inches). (Plunket safe sleep guidelines)

Crib mattresses are thicker — usually around 5–6 inches — but they’re also built to handle more weight and use. Either way, firm matters more than thick. A good test? Press down with your hand. If it feels like a pillow, it’s too soft.

Here’s more if you’re wondering: why are crib mattresses so hard

How to measure a bassinet mattress?

Quick how-to — because guessing never feels great:

1. Grab a soft measuring tape (like a sewing tape).
2. Measure the interior length and width of your bassinet — corner to corner, lying flat.
3. Check depth, too — from bottom to top edge (if you’re replacing a mattress).
4. Use the two-finger rule: once the mattress is in, you shouldn’t be able to fit more than two fingers between it and the bassinet’s sides.

Here’s a quick table of common mattress sizes for reference:

You can also check out how to choose the best crib mattress if you’re navigating both at once.

What size are bassinet sheets?

Most bassinet sheets are designed to fit mattresses around 33” x 15”, but that varies depending on brand and bassinet style.

Common sheet sizes:

• 33” x 15” (standard rectangle)
• 30” x 17” (some ovals)
• 29” x 14” (compact/travel)

Loose sheets? Not worth the risk. Stick to fitted, snug options with elastic all the way around. This guide on crib sheet sizes is helpful if you’re also shopping for cribs.

And if you’re still piecing together your space: essential furniture for nursery

Is a mini crib mattress the same size as a bassinet mattress?

Nope — not even close. They’re totally different setups.

Mini cribs are basically a smaller version of a full crib — good for small nurseries or travel, but way too big for a bassinet frame. One parent shared they tried squeezing a mini crib mattress into a bassinet once — it bowed up and never sat flat. Not worth it.

Here’s the official word if you want the details: CPSC crib mattress regulations

And if you’re curious: what are the measurements of a mini crib mattress

Why are baby bassinet mattresses so thin?

It feels counterintuitive, but thinner is actually safer. A firm, thin mattress (around 1–1.5 inches) helps reduce the risk of suffocation by preventing baby from sinking in. Crib mattresses can be thicker — but bassinet mattresses need to be super stable.

If you’ve ever wondered why crib mattresses also feel rock-hard, this breaks it down: why are crib mattresses so hard

Halo explains the safety side of bassinets pretty clearly too: Halo Sleep bassinet safety