When to Go up a Size in Diapers: A Guide on How to Figure out It’s Time

At some point as a parent or caregiver, you’ll pick up your giggling or crying baby to find a surprise. A diaper blowout … and now, that blowout is on your shirt, the bedding, the bouncer, the swing, the car seat, or wherever else the baby might have been.

Almost everyone will experience a leaking diaper sooner or later. While you might be caught off guard the first time, you’ll know the signs the next time it happens and take proper evasive action.

A little prep work ahead of time can save lots of scrubbing and cleaning later, and oftentimes all you need to do to avoid any of this is to know when it’s time to go up a size in diapers.

A stack of clean diapers on top of each other, on a white background

Pampers swaddlers, Huggies little snugglers … choices, choices, choices! All diapers that have stood the test of time and are proven to be gentle and effective on a baby’s skin.

You’ll start potty training your little one before you know it, so get on top of things as early as possible, get that baby registry all in order before you’re done with your pregnancy, and be prepared for what’s to come!

How To Figure Out Disposable Diapers

In the days of blissful ignorance before parenthood, you may or may not have realized that these things come in all sorts of different sizes. They aren’t manufactured with a “one size diaper fits all” approach.

Each brand fits a little differently, but most are grouped by weight. (You don’t want to rely on having to go to the doctor’s each and every time you want to figure out how much your little one weighs, so get a baby weight scale you can use at home for that purpose).

Some brands are tighter across the bum, some are tighter in the thighs, and some may seem larger than others.

Think of these as size guidelines. They aren’t set in stone, and your baby might need to wear a different size than his or her weight indicates. If your baby is chunky, really long, or extremely active at a young age, you might want to go up a diaper size.

Early on, many rookie parents may buy too many nappies that are small and regret doing this later. Fortunately, you can typically return these if they are unopened and exchange for something bigger.

It’s difficult to predict exactly how many you will need, so it’s best to be flexible and play it by ear.

Remember, sizes are grouped by weight, not by age. A size 1 diaper isn’t necessary for a one-month-old or a one-year-old.


Preemie diapers are made to fit even the smallest babies, those weighing less than two pounds. There’s a range of preemie sizes to keep all babies clean and dry.


Most newborn diapers go up to about ten pounds, so unless your baby is a Goliath, these are a good choice.

You probably don’t want more than 2 or 3 boxes though, as your baby will grow quickly and you’ll find yourself needing to get something bigger soon enough.

Size 1

These usually have a weight range of 8-14 pounds. If your baby was large at birth and isn’t even waiting for weight gain to start kicking in, you might skip newborn size altogether.

This is why you don’t want to buy too many until you know what it is exactly you need.

Size 2+

Now that your baby is getting bigger, you should be able to recognize the danger signs it’s time, and know when to buy something bigger.

You can get ones available for toddlers up to size 6 or 7, and specialty diapers are available for older children and adults.

How To Figure Out Cloth Diapers

Just like disposables, cloth diapers come in a variety of sizes as well. Even better, many cloth diapers can be used for a variety of sizes.

Some brands also sell expanders and panels to make their products work for larger babies and toddlers, so you don’t have to buy a new stash all over again.

If you have a hand-me-down stash, your collection might be an eclectic mix. Read the tags if you still can (hopefully they haven’t disappeared from all that washing) or research the brand to remember.

There are LOTS of cloth diapers out there so you might have to use a bit of trial and error to see what would fit your baby and what doesn’t.

Several measurements can help customize cloth diapers:


Go around the baby’s waist, usually about an inch or so below the belly button. For the cover size, measure over the diaper at the waist.


Measure around the natural crease in your baby’s upper thigh (between the thigh and hip). This won’t necessarily be the chunkiest part of the legs.


Measure from the back (at the waist), up the crotch, to the waist. Remember, it should be about an inch below the belly button.

If you prefer to use sized cloth diapers, each brand may vary a little. Use your measurements from above and check with the manufacturer’s recommendations.

As a general guideline, newborn or XS cloth diapers correspond with newborn or size 1 disposables.

Small cloth diapers are comparable to size 1 or 2 in disposables. Mediums are size 2 to 3, larges are size 3 to 4, and extra larges and extra-extra larges go all the way up to size 7.

For brands that are one-size-fits-most, you’ll likely find an assortment of snaps and buttons. It may take a few tries for you to figure out a combination that is comfortable and leak-proof.

How To Know When To Go Up A Size In Diapers?

You’ll know it’s time as soon as you start to see signs that the diaper is too tight.

Your baby will usually let you know! Look for these things when getting your baby’s diapers changed.

Sign #1

Check your box or read the tag on your cloth diapers. If your baby weighs 18 pounds, she’s probably too big for size 1.

If you notice clothes are getting too tight, it might be time to reassess nappies as well.

Sign #2

Determine if the diaper is on too tight. If you fasten the Velcro too tightly or snap a cloth diaper too tightly, your baby may experience leaks.

The diaper can be so tight that poop is forced up and out the back, instead of settling where it should. If it’s too tight, loosen the diaper. If you can’t loosen it anymore, it’s time to go for something bigger.

Sign #3

Is the diaper no longer covering your baby’s bottom the way it used to? If so, that’s an open invitation for leakage.

If all else fails to get proper coverage back, it’s time to move up a size and get a new set that covers their bottom as needed.

Sign #4

Look for red marks or signs of chaffing. If you wear tight socks, they probably leave a red ring on your ankles.

These same kinds of marks on your baby’s waist or thighs can also indicate that the diaper is too small and it’s time for a size diaper increase.

Sign #5

Blow outs and leaks are happening more often. While sometimes a truly spectacular bowel movement can leak, you shouldn’t have blowouts all the time.

If it seems like poop or urine constantly start leaking, you might try sizing up to solve that.

Sign #6

Whatever brand you’re using at the time, check the weight range of the next size. (Resources exist on the internet, such as this and this, that help guide you about different weight ranges for different diaper brands).

Parents and caregivers notice that going by the next size’s starting weight makes for a much better fit than going by the current diaper size ending weight.

What Happens If I Don’t Change My Baby’s Diaper Size When I Should?

Having your baby wear diapers that are the wrong size and fit is like wearing shoes that are too small.

Nappies that are too tight can cause a whole host of issues, ranging from increased diaper rash and infections, to red marks and even bruises.

Even if you have half of a box left over, it’s better to size up before your baby becomes uncomfortable or suffers from health issues. Compromising their comfort is a terrible idea.

Just like you would do with a used breast pump, used cloth diapers can also be sold or donated. If you prefer, you can consider only donating the unused diapers or pass them along to a family member or friend.

What Happens If I Size Up On My Baby’s Diapers Too Soon?

If you’re worried you rushed the process too soon and went up a size with your baby’s diapers before they needed it, don’t worry, you haven’t flushed your money down the drain.

Sooner rather than later, your baby’s going to need these. So, whether they’ll need to use them or not is not up for debate – they will need them – it’s just that you’ve bought them earlier than needed.

And, as we already mentioned, keep hold of the receipts for whatever boxes or bags of diapers you buy, in case you need to return them for an exchange before putting them to use.

Wrapping Up

Diapering can seem overwhelming at times, even if you’ve changed a hundred of them so far in your parenting/care giving journey.

Leaks and blowouts and a nasty diaper rash doesn’t have to be the norm. To avoid messes and health issues, make sure you’re choosing the right diaper size, and be sure to size up when needed.

Your little one will be growing really fast, sometimes even right before your eyes. They’ll be reaching development milestones before you know it, and you have to keep up with their needs as they grow.

The next time you notice red marks, leaks, and wet spots on your furniture or baby gear, you know what to do – go up a size!

Don’t worry about old ones going to waste, as you can always donate them to someone you know or to a local diaper bank for parents who need them, or sell them later.

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