Setting up a crib for a newborn comes down to one principle: a bare, firm, flat sleep surface with nothing else inside. The safest crib has a tight-fitting mattress, a single fitted sheet, and zero extras. Getting the details right, from mattress height to where you place the crib in the room, makes a real difference in keeping your baby safe during sleep.
Start With the Mattress Height
Most cribs have three or four mattress height settings controlled by adjustable hardware on the frame. For a newborn, set the mattress to the highest position. This is the correct setting for any baby who can’t yet sit up on their own, which covers roughly the first four months. The highest position makes it easier for you to lay your baby down and pick them up without straining your back, and since a newborn can’t pull up or roll out, there’s no fall risk at this height.
You’ll lower the mattress as your baby hits new milestones. Move to the middle setting once your baby can sit independently, commando crawl, or get up on hands and knees, typically around six months. Drop to the lowest setting before your baby can pull to standing, which often happens around nine months. The key is to stay one step ahead of each new ability rather than reacting after the fact.
Check the Mattress Fit
A crib mattress that’s too small creates gaps where a baby’s face or body can become wedged. Federal safety standards require that gaps between a full-size crib mattress and the crib walls not exceed one and a half inches (about 3.8 cm). The simplest way to test this: push the mattress tightly into one corner and check the opposite sides. If you can fit more than two fingers between the mattress edge and the crib wall, the mattress doesn’t fit that crib.
Full-size cribs have standard interior dimensions of 28 by 52 3/8 inches. If you’re buying a mattress separately from the crib, match it to those dimensions. Every time you change the sheets, push the mattress into a corner and do a quick gap check, because sheets can shift things slightly over time.
Use Only a Fitted Sheet
The only thing that belongs on the mattress is a single fitted sheet designed for that mattress size. The sheet should pull snugly around all four corners without bunching or slipping. That’s it. No blankets, no pillows, no quilts, no stuffed animals, no sleep positioners, no wedges.
If you’re worried about your baby getting cold, use a wearable blanket (often called a sleep sack) instead of a loose blanket. These zip or snap around your baby’s torso and can’t ride up over their face. They come in different fabric weights for different room temperatures.
A waterproof mattress pad can go underneath the fitted sheet to protect against diaper leaks. Make sure it lies flat and doesn’t change the firmness of the sleep surface.
Items That Are Banned or Unsafe
Since November 2022, crib bumpers and inclined sleepers are banned hazardous products under federal law. This includes padded bumpers, vinyl bumper guards, and vertical slat covers. The only exception is non-padded mesh crib liners, which are not included in the ban. Inclined sleepers, meaning any product with a sleep surface angled more than 10 degrees, are also illegal to sell regardless of when they were manufactured.
Beyond what’s formally banned, keep all of the following out of the crib:
- Pillows and cushions of any size
- Loose blankets, including thin receiving blankets
- Stuffed animals and soft toys
- Sleep positioners or wedges marketed to prevent rolling
These items all create suffocation risks. A newborn who turns their face into soft material may not have the strength or motor control to turn away.
Where to Place the Crib
Position the crib at least two feet from windows, heating vents, window-blind cords, drapery, and wall lamps. Keep it at least one foot from walls and furniture. Window blind cords and curtain strings are strangulation hazards, so if the crib is anywhere near a window, make sure cords are cut short or secured well out of reach.
Avoid placing the crib next to a radiator, space heater, or heating vent that blows directly on the sleep area. Overheating is a known risk factor for sleep-related infant deaths. A room temperature comfortable for a lightly dressed adult (around 68 to 72°F) is generally right for a baby in a sleep sack.
If you hang a mobile above the crib, remove it once your baby can push up on their hands and knees. The same goes for any crib gym or decorative item strung across the top of the crib.
Always Place Baby on Their Back
Every time your baby goes into the crib, whether for nighttime sleep or a nap, lay them on their back. Back sleeping is the single most important thing you can do to reduce the risk of sudden infant death. This applies even if your baby seems to prefer their side or stomach. Once your baby can independently roll from back to front and front to back, you don’t need to reposition them during sleep, but always start them on their back.
Assembling the Crib Safely
Follow the manufacturer’s instructions exactly. Don’t substitute hardware, skip steps, or modify the crib in any way. After assembly, check every bolt, screw, and bracket for tightness. Wiggle the frame to confirm nothing is loose. Slats should be firm and evenly spaced with no gaps wide enough to trap a limb or head.
Run your hands along all interior surfaces. Feel for splinters, rough edges, cracked wood, or protruding hardware. If any slat is loose, cracked, or missing, don’t use the crib until it’s repaired with manufacturer-approved parts.
Make it a habit to re-check hardware every few weeks. Cribs get jostled from regular use, and bolts can loosen over time.
Buying or Borrowing a Used Crib
Used cribs can be safe, but they need extra scrutiny. First, check whether the crib has been recalled. Go to SaferProducts.gov and search the brand and model number. You can also search recall listings directly on the Consumer Product Safety Commission’s website. If you can’t find the model number or manufacturer, that’s a reason not to use it.
Drop-side cribs, which have a side rail that slides up and down, were banned in 2011 after dozens of infant deaths. If a secondhand crib has a drop side, don’t use it regardless of its condition. Also verify that the crib comes with all original hardware and instructions. Improvising with non-original screws or bolts compromises the structural integrity of the frame.
Test the mattress fit with any used crib especially carefully, since older cribs may have slightly non-standard dimensions. If you can’t find a mattress that fits snugly, the crib isn’t safe to use.
Quick Setup Checklist
- Mattress: firm, flat, fits snugly with no gaps larger than two finger-widths
- Bedding: one fitted sheet, nothing else
- Mattress height: highest setting for newborns
- Crib interior: completely empty (no bumpers, toys, blankets, or pillows)
- Hardware: all screws and bolts tight, no missing or substituted parts
- Placement: two feet from windows, vents, and cords; one foot from walls
- Recall status: verified on SaferProducts.gov
- Sleep position: always on their back