There’s nothing sweeter than the sight of your baby snoozing peacefully. But behind that precious moment is a lot of love, thought, and care. From room temp to bedtime routines, every little detail matters. One of the most important? Finding a baby sleep bag that fits just right.
That’s where our Sleepy Bags come in: a safe sleep solution for babies that combines softness, comfort, and security with adorable prints your fam will love.
In this guide, we’re breaking down everything you need to know about how a baby sleep sack should fit, from sleep sack sizing by weight and height to when to size up a baby sleep sack so you can feel confident at bedtime, every time.
What Is a Sleepy Bag?
A Sleepy Bag is our take on the bamboo baby sleep sack — a wearable blanket made from buttery soft, breathable Lunaluxe® Bamboo. It's TOG-rated for comfort across seasons and designed to keep your little one cozy without the risks associated with loose bedding.
Think of it as the perfect mix of cozy and safe: a TOG-rated sleep bag that helps regulate temperature and supports natural movement without compromising on safety. It’s also a hip-friendly baby sleep sack, with enough room for healthy leg positioning and plenty of wiggles.
Featured Styles: Heather Gray Sleepy Bag and Blue Rainbows Zippy
How Should a Sleep Sack Fit?
Fit is everything when it comes to safe sleep solutions for babies. The right fit means better sleep for your little one and peace of mind for you. Here's what to know about how a sleep sack should fit:
• Neck Opening: The sleep sack neck and arm fit should be snug enough to keep baby from slipping inside, but never tight or restrictive.
• Armholes: These should allow free movement without gaping or falling off shoulders.
• Body: Look for room to kick and wiggle — a key feature in hip-friendly baby sleep sacks.
• TOG Rating: Choose a TOG based on your home’s temp. Our breathable Lunaluxe® Bamboo helps regulate body heat to prevent overheating.
If you’re asking yourself, “How to tell if a sleep sack is too small?”, check the armholes, neck opening, and zipper ease. A proper fit supports both baby sleep sack safety and a comfy night’s rest.
Sleep Sack Sizing by Weight and Height
We know babies grow *so* quickly, which is why we designed our Sleepy Bags with adjustable under arm snaps to grow with them. To make sure you find the right fit, we recommend referencing our baby sleep bag size chart before purchasing. Here's a quick look at the sleep sack size chart by height and weight:
• 0–6m: Fits 8–17 lbs and 21–27”
• 6–18m: Fits 17–26 lbs and 27–32”
• 18–36m: Fits 26–35 lbs and 32–39”
Click here to view our full baby sleep sack size guide.
This chart takes the guesswork out of proper baby sleep sack sizing, helping you find a sleep bag that fits baby safely.
Sleep Sack Fit Tips for Newborns, Infants & Toddlers
Newborns
Follow newborn sleep sack sizing tips closely. Pay special attention to the sleep sack neck and arm fit as that’s key for safe sleep. Opt for TOG 0.5 or 1.5 depending on your room temp.
Infants
Look for a little extra legroom. Infants need space to wiggle and move — just make sure they’re still within the recommended weight and height range.
Toddlers
Ready to stretch and move more independently, toddlers benefit from a bit more space. If your little one is near the top of their size range, it may be time to size up.
When to Size Up (or Not)
Curious about when to size up a baby sleep sack? Here are some signs:
Size up if:
• Baby has outgrown the listed sleep sack size chart by height and weight.
• The armholes are too snug or the zipper is hard to close.
• Baby looks uncomfortable in the Sleepy Bag.
Don’t size up just because:
• It looks long. Extra length in the body is perfectly normal (and safe!).
• You want it to “last longer”. An oversized neck or armhole isn’t safe.
Which TOG Rating Should You Choose?
We’ve broken down TOG ratings in more detail in this article, but here’s a quick rundown of how to choose between the three TOG ratings available for our baby sleep bags.
• Lightweight – 0.5 TOG, best for room temperatures 74° - 78° F
• Seasonless – 1.5 TOG, best for room temperatures 68° - 74° F
• Winter Weight – 2.5 TOG, best for room temperatures 61º - 67º F
Why Parents Love the Sleepy Bag
We’re not the only ones obsessed with our baby sleep sacks… check out these reviews from caregivers in our LS fam!
“Best sleep sack ever! We've tried a ton. This is the best material, weight, and love how it can grow with her.” ~ Elizabeth H.
“I ordered this for [peace] of mind. I love that I can keep my baby warm at night without worrying about [a blanket] getting on her face. Great quality and she sleeps very well with it!” ~ Jacqueline L.
“First time purchasing a sleepy bag, but it will not be the last. Super soft and has the magic touch to help my baby sleep through the night” ~ Harley R.
“We have tried countless brands of sleep bags and LS is by far the softest, comfiest and best quality bag we have found! Our daughter loves to wear it every night to bed!” ~ Meral A.
“Absolutely love this sleep sack and so does my baby! Not sure how I’ve [gone] so long without this sleep sack for my baby. He’s 9 months old, 19lbs and 28’ long, we got the 6-18 months and it fits perfectly with so much room to grow. He sleeps so good with it. I opted for the light weight and it’s perfect. I’ve bought 3 so far and plan to buy a few more for back up. Seriously if you’re thinking about getting one you won’t regret it! Your baby will sleep so good with this sleep sack.” ~ Virginia B.
Featured Styles: Check Mates Sleepy Bag and Heather Oatmeal Ribbed Zippy
Safe, Snug & Made for Sweet Dreams
With the right fit, your baby can rest safely and you can rest, too, knowing your little one is safe and secure. Little Sleepies Sleepy Bags are thoughtfully designed with baby sleep sack safety in mind, combining adorable style with cozy, sleep-friendly functionality.
So whether you’re figuring out how should a baby sleep sack fit, or looking for a durable, buttery soft bamboo baby sleep sack to grow with your little one, we’ve got you covered.
Shop Sleepy Bags now and make bedtime a breeze!
Want to learn more about baby sleep safety? Check out these helpful guides:
How to Swaddle a Baby: A Simple, Safe Guide for New Parents
