There is very little in parenting that tests you like a cloth nappy that leaks twenty minutes after you changed it. You did everything right. You wiped, you dried, you fastened. Then the wet patch appears anyway. Welcome to figuring out leaking nappies 101! The good news is that most leaking nappies can be fixed once you know what is actually going wrong. Sometimes bub has outgrown the nappy and it is time to size up cloth nappies. Other times the fit is fine and the real issue is absorbency, which means you need to boost the nappy instead. Working out which one you need comes down to fit, absorbency, and comfort. It does not come down to age or weight alone. Every baby is built differently, so the way a nappy sits on your bub will always matter more than the number on the packet.
Leaking Nappies 101 – Size Up or Boost? Understand the Difference
When a nappy leaks, there are two main explanations. The first is a fit problem. If the nappy is too small, there will be gaps around the legs, the waist will sit too low, and the snaps or tabs will be doing more work than they should. Leaks in this case usually escape around the edges of the nappy. The second explanation is an absorbency problem. The nappy fits correctly, sits where it should, and leaves no red marks, but bub simply wets through it faster than the nappy can hold. The leak tends to happen in the middle of the nappy because the core is full. Understanding this difference is the key, because the two problems need very different fixes. A too-small nappy should be replaced with the next size up. A nappy that fits but lacks absorbency needs a booster added until you find a better solution.
Signs It Is Time to Size Up Cloth Nappies
Your cloth nappy can tell you a lot. Watch for these signs that your bub has outgrown the current size or its time to adjust your rise snaps to a larger size.
Frequent Leaks or Blowouts
If leaks are becoming a regular event, especially around the edges of the nappy, that is one of the clearest signs it is time to size up or adjust your rise snaps in cloth nappies. Blowouts are also a clue. When a nappy is too small, there is less room for the absorbent core to expand, and mess escapes at the sides or up the back. If changing the nappy more often has not solved the problem, check the fit before you add more absorbency.
Red Marks Around the Legs or Waist
Red marks around your baby’s legs are a classic sign that the nappy is too tight. You should always expect a few gentle pink marks from elastics after removing a nappy (similar to what you get from wearing a bra or belt all day), but deep red impressions that linger mean the nappy is digging in.
Struggling to Fasten the Tabs Comfortably
When the tabs or snaps become a battle, listen to them. If you are stretching the tabs to their limit, or the front of the nappy barely reaches the waistband, the fit has been outgrown. Tabs should fasten easily and sit without strain. Struggling to fasten the tabs comfortably is one of the most straightforward signs that you need to move to the next size setting or larger size nappy.
The Nappy Is Sitting Too Low
A cloth nappy should sit just below the belly button. If it is sitting too low, you have a sizing problem. A low-sitting nappy leaves less space for absorbency where it counts and creates gaps around the legs. If you find yourself constantly pulling the nappy back up, it is time to size up.
The back of the nappy should sit at least a few cm above the butt crack to keep everything contained. The front & back waist level should be the same height.
Check the Waist and Leg Seals
Gaps in the leg seals are another sign that the nappy is too big or the wrong fit. The leg elastic should hug your baby’s leg gently to keep everything inside. When the nappy is outgrown or on the wrong size, the leg seals cannot do their job, and leaks find their way out. Checking the waist is just as important. If you cannot get a snug fit at the waist without over-tightening, the nappy is no longer the right size.
Read the Size Guidelines for a Starting Point
Nappy sizing guides exist for a reason, but they are only a starting point. If you have ever tried reading the size guidelines on the side of a box of nappies, you have probably noticed just how tricky sizing can be. Tall & slim V smaller and chunkier can be the same weight, but need a different size. Use the weight ranges as a rough guide, then trust what your eyes and hands tell you. If the nappy meets bub’s needs in fit and comfort, you can stay in the current size a little longer. If it does not, size up even if the weight range suggests otherwise. We have nappies that fit up to 30kg for older kids when you get to that stage.
When to Boost Instead of Size Up
Sometimes the nappy fits beautifully but bub is still leaking. This is where boosting comes in. Adding a booster or insert increases absorbency without changing the fit drastically. This is especially useful at night, for heavy wetters, or during growth spurts when bub’s output changes faster than their waistline. If you are building a stash that handles heavy wetters and overnight use, fitted nappies made from bamboo or hemp are worth adding to the rotation, along with boosters in the same bamboo and hemp blends from the Baby Beehinds range. As these are the most absorbent type of boosters to boost your nappies and most of them are interchangeable between cloth nappies in Australia.
There is a limit, though. Once newborn nappies cannot take more inserts without compromising the fit, it is time to move to larger nappies. If you add a booster and the nappy no longer closes properly, or the fit becomes bulky and gappy, you have crossed the line from boosting into sizing up. The booster should disappear into the nappy, not stretch it out of shape.
Growth Spurts and the Right Moment to Switch
Babies grow in fits and starts, and nappy sizes can change unexpectedly. A growth spurt can turn a comfortable nappy into a tight one overnight. A useful rule for baby clothes is that if an outfit is tight in two places, it is time to go up a size. The same logic works for nappies. If you spot tightness during a growth spurt, check the nappy fit and be ready to size up cloth nappies sooner than you planned.
Your baby’s body shape matters too. If your bub has a longer torso, you will likely need to size up earlier or use extenders to get more length. If your baby is shorter, the standard fit might last longer. There is no universal age for moving between sizes because every baby is different. What matters is how the nappy fits on your specific bub.
How Many Cloth Nappies Do You Need in Your Stash?
While you are working out the right size, it helps to know how many nappies you actually need. Most families need somewhere between 15 and 25 reusable nappies. Starting with 15 is a good idea, and you can always add more to your stash if you find yourself running out between washes. A bigger stash also gives you more flexibility when it comes to washing and drying so we think 24 is the sweet spot, but at a minimum 15 to go full time.
Final Thoughts on Fit, Absorbency, and Comfort
Leaking nappies are rarely a mystery once you understand what to look for. If the nappy is too small, you will see red marks, struggling tabs, a low-sitting waist, and leaks around the edges. That is your cue to size up cloth nappies. If the nappy fits well but bub is wetting through the core, add a booster or insert until the nappy can no longer hold more without compromising the fit. From there, it is time to move up a size. Baby Beehinds has been helping Australian families with reusable cloth nappies for over 22 years, and the award-winning range includes all-in-one, all-in-two, and fitted nappies, plus wet bags, liners, boosters, and reusable wipes to support you at every stage.
Frequently Asked Questions
How do I know when to size up cloth nappies?
Look for frequent leaks or blowouts, red marks around the legs or waist, tabs that are hard to fasten, and a nappy that sits too low instead of just below the belly button. Check the waist and leg seals for gaps. Sizing depends on fit, absorbency, and comfort, not just age or weight.
Why does my cloth nappy leak if it fits well?
If the nappy fits comfortably without red marks or gaps but bub still wets through, the issue is absorbency, not size. Add a booster or liner to increase how much the nappy can hold. Once the nappy cannot take more inserts without compromising the fit, it is time to move up to a larger size.
How many cloth nappies do I need?
Most families need somewhere between 15 and 25 reusable nappies. Starting with 15 is a good idea, and you can always add more to your stash if you need extras between washes. Having a few spare nappies also helps when bub is between sizes during a growth spurt.
Do cloth nappies change what size clothes bub wears?
Sometimes. If your baby has a longer torso, you may need to size up clothes earlier or use nappy extenders to gain extra length. If your baby is shorter, standard sizes may fit fine. During growth spurts, check clothes and size up when an outfit is tight in two places.
