Think upping a size helps sleep bags fit your baby for longer? Think again! While this trick might apply to clothes, the perfect sleep sack sizes is a “snug fit”.
The reasons all boil down to safety. An oversized sleep bag can cause your little one to slip down inside, posing a risk of suffocation. An overly tight one, on the other hand, can sacrifice comfort and can restrict the baby’s growth.
So, how do you select the correct size? Don’t fret, parents! SwaddleAN will explain the importance of sizing, along with a detailed guide on choosing the right sleep bag size to ensure your baby’s comfort and safety.
Why is Sleep Sack Size So Important
The Safety Risk of a Sleep Sack That’s Too Loose
Tossing, turning, kicking, and squirming, your little one never stays still while sleeping. If the neck and armholes are too wide, even a slight movement can make the sack slip over the baby’s face.
Once their nose and mouth are both covered, there’s a high risk of suffocation. So, the last thing you want to do is to choose an oversized sleep bag for your kiddo. This is one of the most important sleep sack safety rules.
The Discomfort from a Sleep Sack That’s Too Tight
An overly small sleep sack is just as hazardous as an oversized one. For one, the limited space might cause overheating and discomfort, disrupting a baby’s sleep.
Worse yet, a sleep bag that’s too tight restricts a baby’s nighttime movements, especially hips and legs. This takes a toll on the growth of these parts in particular and the motor development in general.
According to the American Academy of Pediatrics (AAPs), wrapping a baby’s legs too tightly can lead to hip dysplasia (hip dislocation, to put it simply).
The Impact on Temperature Regulation Efficiency
The correct size can make a difference in regulating temperature effectively. An oversized sleep sack leaves too much air inside, reducing its ability to warm.
Meanwhile, one that’s too tight hinders the airflow and traps heat inside, increasing the likelihood of overheating. The proper temperature can be the difference between a solid night of sleep and restlessness.
A Guide to Measuring and Choosing a Standard Size
Always Prioritize Weight and Height, Not Age
Every baby grows differently; it’s totally okay for a 1-month-old to weigh 8 pounds or 10 pounds. So, it’s not their age but their height and weight that matter when choosing the right sleep sack size. Our advice is to check these measurements before getting a sleep bag for your little one.
How to Check the Fit of the Neck and Armholes
Weight and height aside, you must ensure the chosen sleep sack really fits your baby’s body by checking the neck and armholes:
- For the neck opening: It must embrace the baby’s neck snugly. It should neither be able to pull up over the chin easily nor leave marks on the neck. The sweet spot is that it has enough space to slide two fingers inside.
- For the armholes: They should fit nicely with some room for easy movements, but not to the point that the baby can easily slip their arms through these openings.
Checking for Leg Room
Most babies sleep with their legs scrunched up, right? But that doesn’t mean the sleep bag should fit this position. Your little one might stretch and kick at times, so they need some space for their movements and development, as well.
Quick tip: A rule of thumb is to leave about 4 inches for the legroom so your baby can curl up or stretch out freely.
Shop SwaddleAn Sleep Sacks Designed for Baby's Healthy Development
SwaddleAn’s Size Chart and Cross-referencing Guide
Here’s a sleep sack size chart based on our research and customer feedback:
| Size | Age (reference only) | Weight | Height |
| S | 0-6 months | 9-18 pounds | 23-28 inches |
| M | 6-18 months | 18-26 pounds | 27-33 inches |
| L | 18-36 months | 26-35 pounds | 32-38 inches |
Real-life Examples
As we shared earlier, no two babies are the same, so there’s no one-size-fits-all sleep sack. Consider their height and weight to choose the best fit.
For example, your little one is only 5 months old but weighs 18.7 pounds (8.5 kg) and is 27.5 inches long (70 cm). Instead of going for a size S based on age recommendations, it’s best to go up a size M for optimal comfort and longer usage.
Or, if your 7-month-old one is on the smaller side, weighing just 15.4 pounds (7 kg), you should continue using the size S to ensure snug fit around the neck and armholes.
When to Transition to the Next Size?
There are two easy signs to tell when to upsize the sleep bag. First, if you notice your baby’s legs almost touch the bottom of the sack, it’s time to get the next size. Another sign is when the bag gets too tight around the chest and armholes. This means that , your baby has outgrown it. Here's an example:
My LO is 27 inches long and weighs about 14.5 pounds. A size S seems a bit short for her, but I’m afraid a size M might be
too loose. Any recommendations?
Our answer: A sleep sack is only “too loose” when it can easily slip over the baby’s face. If this is your case, we recommend opting for a size S for safety. If not, you can still go for the size M to ensure ample legroom for your little one. The size S might fit her torso, but the restricted legroom will leave her uncomfortable.
If you need the exact circumferences of the neck opening and armholes to check with your baby, don’t hesitate to reach out to Swaddle An!
Frequently Asked Questions About Sizing
Should I buy a larger size so my baby can use it longer?
No. For the sake of safety, NEVER buy an oversized sleep sack for your baby.
Do sleep sacks shrink after washing?
Organic sleep sack material like cotton can shrink a bit after the first wash. Our size chart has taken this shrinkage into account. Follow the washing instructions to keep the best shape.
What to do if my baby is between two sizes?
Prioritize your baby’s weight when choosing a sleep bag size. If they reach the minimum weight of the bigger size, it’s time to upsize. But if their weight still falls between the range of the smaller size, continue using the smaller one for safety.
Sweet Dreams, Little Ones!
Choosing the correct sleep sack size is more important than some parents think. It’s the key to ensuring the safety and improving the sleep quality of your little one. Remember to prioritize weight and height over age and check if the neck and armholes fit snugly.
Refer to SwaddleAn’s sleep sack sizes chart, and you can pick a suitable sleep sack for your little one’s optimal safety. Ready to find the perfect size for your baby? Check out our sleep back collections for personalized stuff! Custom fit and safety guaranteed!
Related Blog Post
What is TOG: 3-Step Guide on TOG Rating to Keep Your Baby Safely Warm
Picking the Perfect Baby Sleep Sack for Different Seasons
7 Smart Features to Look For When Buying a Baby Sleep Sack
Sources
- Practice safe swaddling to protect baby’s hips: https://publications.aap.org/aapnews/article/32/9/11/9561/Practice-safe-swaddling-to-protect-baby-s-hips