Everything parents need to know before buying a crib mattress — standard sizes, firmness, materials, and safety basics, from LA Mattress Store.
Choosing a crib mattress feels like a small decision compared to picking out a crib or a car seat, but your baby will spend more hours on that mattress than on almost anything else you buy. A well-chosen crib mattress supports safe sleep and lasts through years of naps, diaper changes, and the occasional overnight blowout. Here's what actually matters when you're shopping for one.
Nearly all cribs sold in the U.S. use a standard size, so the good news is you don't have to measure much. A standard crib mattress is about 27.25 inches wide by 51.25 inches long, with a maximum thickness of about 6 inches. That standardization exists for a safety reason: a mattress that's too small leaves gaps along the crib rails where an infant could become trapped.
Mini cribs and portable/travel cribs use a smaller mattress, typically around 24 by 38 inches, so always check your crib's manual before buying rather than assuming "crib size" means one universal thing.
This is the one place where a crib mattress is genuinely different from every other mattress in your house. A firm, flat sleep surface is the standard safe-sleep recommendation for infants, not a soft, plush one. When you press down on a crib mattress, it should barely give, and it should spring back to its shape quickly. If you can dent it slightly with your hand and the dent lingers, it's too soft for a crib.
Crib mattresses generally come in two types:
Foam crib mattresses are lighter (easier for 3 a.m. sheet changes), often more affordable, and available in a range of densities. Look for a firm, high-density foam rather than a soft memory foam, memory foam's slow-recovery feel is designed for adult pressure relief, which is the opposite of what a crib needs.
Innerspring crib mattresses use a coil count (often 80-150 coils) plus a firm foam or fiber layer on top. More coils generally means a more even, consistently firm surface, though quality of materials matters as much as the number.
Look for a mattress with a wipeable, waterproof cover, usually a laminate or vinyl-alternative surface. This isn't just about convenience, a cover that keeps moisture out of the mattress core matters for hygiene and for the mattress holding its shape over time. Two-stage mattresses (firmer on one side for infants, slightly more cushioned on the flip side for toddlers) are worth considering if you plan to use the same mattress through the toddler bed transition.
Once the mattress is in the crib, you shouldn't be able to fit more than two fingers between the mattress edge and the crib frame on any side. A gap larger than that is considered unsafe and is one of the most common reasons a crib mattress needs to be replaced or swapped for the correct size.
If you're setting up a nursery anywhere in Los Angeles, our showrooms carry firm, safety-focused mattress options and our team can walk you through sizing for your specific crib. We offer same-day delivery across our five LA-area locations, so a new crib mattress doesn't have to mean a long wait before baby's room is ready.
A standard full-size crib mattress measures about 27.25 inches wide by 51.25 inches long, with a maximum thickness of roughly 6 inches. Mini and portable cribs use a smaller mattress, so always check your specific crib's requirements first.
Full-size cribs are built to a standard size, so most full-size crib mattresses are interchangeable. Mini cribs, portable cribs, and bassinets, however, each use their own smaller mattress sizes, so "crib mattress" isn't a single universal size.
Usually not. Most cribs are sold separately from the mattress, since sizing and firmness needs can vary by brand and by family preference. Budgeting for the mattress as its own purchase will save you a surprise at checkout.
Most guidance is to lower the mattress once your baby can sit up unassisted, and lower it again to the lowest setting once they can pull themselves to a standing position, since a higher mattress makes it easier for a mobile baby to climb or fall out.
Take our quick sleep quiz to get matched with the right mattress for your household, or stop by one of our LA showrooms to feel the difference between crib mattress firmness levels in person. For the rest of the family's sleep setup, see our guides on buying the perfect mattress for your baby, choosing a mattress for kids or teens, and our best mattress for kids buying guide, plus our foundations and bases collection if you need a supportive base for the rest of the bedroom.
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