When to lower the crib mattress

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This article is general crib safety guidance aligned with AAP and CPSC standards. If your crib model has specific instructions, follow those.

Why crib heights exist

Cribs have adjustable mattress heights because babies grow and become mobile in stages. The highest setting is for the newborn-to-3-month phase when you're reaching over the rail constantly. The middle is for the sitting-and-rolling phase. The lowest is for the standing-and-climbing phase.

The safety logic: as babies become taller and more mobile, the distance from the mattress to the top of the rail needs to grow so they can't flip over.

The 3 mattress settings

Highest setting: Birth to about 5 months

The mattress sits close to the top of the crib (typically 4 to 6 inches below the rail in this position). Easy on your back when lifting a newborn in and out.

Use until baby:

• Pushes up onto hands and knees (rocking, pre-crawling)
• Rolls reliably from back to front in the crib
• Pushes up on extended arms during tummy time
• Is about 5 to 6 months old

Middle setting: 5 to 9 months

Mattress drops to roughly the middle of the crib. Rail is now about 14 to 18 inches above the mattress. Most babies use this height from rolling to early standing.

Move to the lowest setting when baby:

• Pulls to stand against any vertical surface
• Can grip the crib rail and pull up
• Is about 8 to 10 months old (even if not yet pulling to stand)

Lowest setting: 8 months to about 24 to 36 months

Mattress is at its lowest position. Top of mattress should be at least 26 inches below the top of the crib rail (the federal standard).

Use the lowest setting until baby:

• Is 35 inches tall (the typical crib outgrow height)
• Attempts to climb out
• Is around 2 to 3 years old

At that point, transition to a toddler bed.

The "wait until they show the skill" rule

The mistake parents make: lowering the mattress because of age, not skill.

The right cue is the skill. If your 4-month-old is rolling and pushing up on hands and knees, drop the mattress now. If your 7-month-old shows zero standing intent yet, you don't have to drop to the lowest setting yet.

Some babies skip the middle setting entirely — they go from highest to lowest in one move because their pull-to-stand happened the day after their rolling-from-back-to-front. That's fine.

The danger of waiting too long

Crib-related injuries spike around 9 to 12 months because that's when:

• Babies are tall enough to grab the rail
• Strong enough to pull themselves up
• Not yet smart enough to control the climb back down

A standing baby in a too-high-mattress crib can:

• Topple forward over the rail
• Get a leg stuck between the rail and the mattress
• Fall back and hit their head on the rail

The CPSC tracks crib injuries closely. Many are mattress-height issues.

How to lower the crib mattress (without taking it apart)

Most cribs have a U-bracket or shelf system. Steps:

1. Remove all bedding from the crib.
2. Lift the mattress out entirely.
3. Find the mattress support frame. This is the metal or wooden frame that holds the mattress.
4. Move the support frame's brackets or pegs to the next set of holes (usually one set of holes lower).
5. Re-secure the brackets. Most use bolts with locking caps.
6. Verify the support is solid by pressing down on each corner before putting the mattress back.
7. Place mattress back in. Test for snug fit — your fingers should not slide between mattress and crib sides.

Most cribs come with the right tool included. If you've misplaced it, an Allen wrench or socket set will work. The whole process is 10 to 15 minutes.

Common questions

"Is the mattress too low now? I can't lift baby out easily."

If you're tall enough to reach in, baby's safety wins over your back. If you genuinely cannot reach in (short stature plus tall crib), use a sturdy stool. Don't compromise on the height for convenience.

"My baby is small for their age. Do I still need to drop the mattress?"

If they have the skill (pulling to stand), yes. Drop the mattress. Pull-to-stand height is what matters, not weight or age.

"My crib only has 2 settings, not 3."

Some cribs (especially mini cribs and some convertibles) have only 2 heights. In that case: highest until pre-crawling, lowest from pulling to stand. Skip the middle stage entirely. This is fine and is how the crib is designed.

"My crib has 4 settings — when do I use the extra one?"

4-setting cribs (some Babyletto, Stokke models) usually have:

• Setting 1 (highest): newborn
• Setting 2: rolling baby
• Setting 3: pre-standing baby
• Setting 4 (lowest): standing baby through toddler bed transition

"What about a crib-to-toddler bed conversion?"

That's a different transition — usually around 2 to 3 years old when toddler tries to climb out or is over 35 inches tall. The mattress stays in the lowest crib position until that transition. See our toddler bed transition guide.

Crib safety checklist beyond mattress height

• No bumpers, blankets, pillows, or stuffed animals in the crib until at least 12 months.
• Mattress fits snugly — no gaps wider than 2 fingers between mattress and crib side.
• Crib slats are no more than 2 3/8 inches apart. The federal standard since 2011.
• Drop-side cribs are banned in the US since 2011. If you have one, do not use it.
• Crib is away from windows, cords, blinds, and shelves baby could grab from inside.
• Mobile is removed by 5 months or when baby can push up to reach it.
• No products that attach to the crib (sleep positioners, side-rail bumpers) per AAP.

When mattress lowering won't be enough

Some toddlers, especially shorter ones, can climb out of a crib at the lowest setting. If that happens (or if they're 35+ inches tall), the crib has been outgrown.

Don't try to "tame" a climbing toddler with sleep sacks that restrict legs (no — climbing-deterrent sleep sacks have safety concerns). Move to a toddler bed or floor bed instead. See when to switch to a toddler bed.

Sources

• CPSC — Crib Information Center
• AAP — Safe Sleep Recommendations
• NIH Safe to Sleep

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The Sleep Desk

Reviewed by a pediatric sleep consultant · Aligned with CPSC and AAP safety standards · Updated May 2026