A standard full-size crib measures 28 inches wide by 52 3/8 inches long on the inside.
That interior dimension is the federal definition set by the U.S. Consumer Product Safety Commission (CPSC), and it dictates which cribs count as “full-size” in this country. But when you search “what is the standard size of a crib,” you may be asking about the overall frame footprint for your nursery layout, the mattress you need to buy, or whether a full-size crib will even fit the room you have. The answer to each of those questions is different, and nailing all three before you buy prevents the two most common nursery mistakes: a mattress that leaves a dangerous gap and a crib frame that won’t fit through the door.
The Official U.S. Standard Crib Dimensions
The CPSC’s standard for a full-size crib is precise. The interior must measure 28 ± 5/8 inches (71 ± 1.6 cm) wide and 52 3/8 ± 5/8 inches (133 ± 1.6 cm) long, measured between the innermost surfaces of the side and end panels.
In practical retail terms, that rounds to roughly 28 inches by 52 inches. Your crib’s actual interior can vary slightly within those tolerance ranges, which is why the mattress fit matters more than the label.
One distinction that trips up many parents: the standard crib mattress size is not the same as the crib’s interior dimensions. The CPSC-linked minimum mattress size cited by major sources is 27 1/4 inches by 51 5/8 inches. The mattress sits inside the crib frame, so it is always smaller than the interior space around it. A mattress must fit snugly with no gaps, because any space between the mattress edge and the crib side can trap an infant.
What Size Crib Fits Your Room?
The interior dimensions tell you what mattress to buy, but the crib’s outer footprint is what determines whether it fits your space.
For tight nurseries, the most common alternative is a mini crib, often around 24 inches by 38 inches. Unlike full-size cribs, mini cribs have no federal size standard, so dimensions vary by model. Some portable and compact cribs run about 26 1/4 inches by 39 1/2 inches, while larger convertible models can reach 54–58 inches long by 28–31 inches wide in crib form.
Before you commit, measure your nursery’s usable length and width, then subtract clearance for doors, drawers, and walking paths. Check the product manual or spec sheet for the exact frame dimensions rather than trusting a category label like “standard” or “mini.”
If you’re weighing options for a tight footprint, our roundup of the best cribs for small spaces compares tested models that actually fit compact rooms.
Measuring a Crib: Inside and Out
A measuring tape settles every question. Here is the order that works:
- Measure the room first. Record the nursery’s usable length and width, then subtract clearance for doors, drawers, and walking paths.
- Measure the crib’s outer footprint. The frame dimensions determine whether it fits; the interior dimensions do not.
- Measure the crib’s inside after assembly. Compare the interior length and width against the mattress. The mattress should sit flush with no hazardous gaps.
- Verify mattress thickness.
The mistakes happen when parents buy a mattress based on label terms alone, or assume every mini crib is the same size. Always verify the inch measurements against the crib manual and the mattress tag or spec sheet.
| Crib Type | Typical Interior Size | Best For |
|---|---|---|
| Full-size (CPSC standard) | 28 in × 52 3/8 in | Most nurseries; the only federally defined size |
| Mini crib | 24 in × 38 in (varies) | Small rooms, shared spaces, compact apartments |
| Portable/compact crib | ~26 1/4 in × 39 1/2 in | Travel or occasional use |
| Convertible crib | 54–58 in × 28–31 in (model-specific) | Long-term use; converts to toddler bed |
CPSC Rules and Crib Safety Basics
The full-size crib definition applies to cribs used in homes, child care facilities, family child care homes, and public accommodations affecting commerce. It does not apply to cribs that are medical devices as determined by the FDA. Non-full-size cribs may be smaller or larger than the standard but must be rigid and must not have mesh sides.
The CPSC’s full-size crib guidance is the authoritative source for the federal specification.
FAQs
Is a standard crib mattress the same size as the crib itself?
No. The mattress is smaller than the interior of the crib. The standard minimum mattress size is 27 1/4 inches by 51 5/8 inches, while the crib interior is 28 inches by 52 3/8 inches. The difference gives the mattress room to sit inside while still fitting snugly with no gaps along the edges.
Do mini cribs use a different mattress size?
Yes. Because mini cribs have no federal size standard, their mattresses vary by model. Some use a standard mini crib mattress around 24 by 38 inches, but portable and compact models can differ. Always measure the crib’s interior after assembly and match the mattress to those exact numbers rather than relying on a label.
How long can a baby sleep in a standard crib?
The actual limit depends on the crib’s weight and height restrictions, which are listed in the manual, and on when your child tries to climb out. Some convertible models extend use by converting to a toddler bed.
References & Sources
- U.S. Consumer Product Safety Commission. “Full-Size Baby Cribs.” Official federal specification for full-size crib interior dimensions.
- Sleep Foundation. “What Size Is a Crib Mattress?” Details standard mattress dimensions and snug-fit requirements.