Crib mattress height depends on your baby’s age, size, and abilities. Newborns and infants who are younger than 5 months old and cannot sit up can generally sleep safely on a crib mattress placed at the highest position. Once a baby can sit up, or is able to roll over or push up onto their hands and knees, you should lower the crib mattress to the halfway position. As soon as your baby shows signs of pulling up to standing, you should lower the crib mattress to the bottom level.
Keep reading to learn the ages and milestones you need to look out for when considering your baby’s crib mattress height.
Crib Mattress Height: Why It’s Important
Indeed, roughly 66% of injuries involve babies falling from a crib or pack n play or bassinet.
These statistics are as sobering as they are eye-opening.
“How you use it” includes choosing the right time to transition your baby from a bassinet or side sleeper to their own crib, not trying to make a pack n play more comfortable with padding, and setting up a floor bed correctly, if you choose to use that Montessori-style for sleeping.
For this article, however, I want to help parents and caregivers understand when they should lower their baby’s crib mattress. Keep reading to find out more.
Crib Mattress Height Regulations
Crib falls injure babies with shocking frequency.
Given how common it is, it’s no surprise the federal government regulates crib mattress height. These guidelines are set-up to create “escape resistant” sleep environments for babies shorter than 35 inches tall.
Once your baby is 35″ or taller, it’s time for a toddler bed, BTW!
In the United States, the minimum distance between the top of the lowest support and the top of the crib side rails is 26 inches.
Most full-size crib mattresses are between 5 and 6 inches thick. This means the actual distance between the top of the mattress and the top of the rails is 20 to 21 inches.
Falls from heights are a danger to babies in other parts of the home, too – that’s why we also don’t recommend a baby bathtub that sits on the counter or on a base.
Our Ages & Stages Guide to Crib Mattress Height
Place Crib Mattresses in the Highest Position for Newborns
As long as your baby can’t sit up and is under 5 months, the highest position is likely safe.
When your baby is a newborn, it’s fine to keep it in the highest position. This will make it easier on your back when you’re lifting baby out of the crib, make it more likely you’ll be able to put your baby down without waking them, and also ensure you’re able to support your baby’s neck properly when lifting in and out of the crib. (source)
As a rule of thumb, you can keep your baby’s mattress in the highest position as long as they’re immobile.
Once they can start moving on their own – this includes rolling and sitting unsupported – it’s time to lower it. You also need to give up swaddling at this point, and focus on dressing them appropriately for their age, abilities, and the season/temperature.
Lower the Crib Mattress to the Middle Height for Infants
Once a baby can sit up by themselves, it’s time to lower the crib mattress.
By the time your baby is able to sit up, roll over, or push onto their hands and knees, you’ll want to have adjusted her mattress to the middle height (one notch down from the highest position).
Most babies are able to sit by themselves between 5 and 8 months of age. Once they’ve mastered rolling and sitting, babies generally work on pushing themselves up onto their hands and knees.
At this stage, the highest position can be dangerous, as your baby may try pulling themselves to standing at any moment. Likewise, they may be going through a sleep regression, insisting on staying away at odd hours, playing by themselves in their crib. You need to lower the mattress height to ensure they’re safe for this stage.
Place the Crib Mattress at the Lowest Position for Older Babies and Toddlers
When your baby shows any signs of pulling themselves to standing, lower everything to the lowest setting.
This will make it harder for your baby to climb out of their crib. Lowering the mattress at the right time reduces the risk of falls and injury.
At this stage, it’s also important to remove any crib bumpers or wedges from the crib.
These items are unnecessary and potentially unsafe at any time. They become particularly problematic once your baby can stand in their crib. Babies can use them as a makeshift staircase to climb out of their crib.
Time for a Toddler Bed?
Once your child tries to climb out of their crib or reaches 35” in height, transition them to a toddler bed. You can also transition them to a toddler mattress at this point, which doesn’t need to be as firm as a baby crib mattress.
When you think your child is ready, you’ll also want to introduce a toddler pillow.
If your toddler is still trying to climb everything in sight, you may want to invest in a toddler-safe climbing toy to direct their energy towards safe climbing. Speaking from personal experience here, but our toddler’s climbing only got under control when we finally broke down and bought a Pikler triangle.
In the United States, roughly 10,000 zero to two-year-olds are treated in the ER every year for crib-related injuries.
Keep your baby safe with this handy crib mattress height cheat sheet.
- Measuring tape
- Tools to adjust your baby's crib (screw driver, Allen key, etc.)
Use the following guidelines to decide when to use each crib mattress height.
Highest Crib Mattress Setting
Keep the crib mattress in the highest position for newborns under 5 months who cannot sit up. As long as your baby can’t sit up and is under 5 months, the highest position is likely safe.
Middle Crib Mattress Setting
Once your baby can start moving on their own – this includes rolling, sitting unsupported, and pushing themselves onto their hands and knees – it’s time to lower the crib mattress.
Most babies reach this stage between 5 and 8 months of age. At this stage, the highest crib mattress position can be dangerous, as your baby may try pulling themselves to standing.
If a baby stands in a crib with a mattress at this height, they could easily fall out of the crib.
Lowest Crib Mattress Setting
When your baby shows any signs of pulling themselves up to a standing position, lower the crib mattress to the lowest setting. Lowering a crib mattress at the right time reduces the risk of falls and injury.
When in doubt, err on the side of caution and ask a child safety expert or your paediatrician what's safest for your family. This information isn't meant to replace expert advice of a doctor or government agency.