When to move up a diaper size: signs the fit is too small

When to move up a diaper size: signs the fit is too small

Move up a diaper size when the fit tells you to, not only when the scale does. The clearest signs are tabs that no longer reach, leaks that start suddenly, deep marks at the waist or thighs, and a diaper that sits low under the belly button. Here is how to read each sign and how to switch without wasting the pack you have open.

The weight range is a starting point, not a rule

The range on the pack is a guide to who the size was made for. Babies grow in length as well as weight, so a long baby can outgrow a size before reaching the top weight, and a growth spurt can change the fit quickly. Treat the printed range as the moment to start watching, then let what you see on your baby make the call. The diaper sizing guide gives a general view, but the range on your own pack is the one to follow.

A quick look at length helps too. With your baby lying flat and the diaper fastened, the back edge should cover the bottom fully and the front should reach up to the waist without being pulled. If either end is short, the diaper is running out of room before the weight range says it should.

Tabs that no longer reach the centre

Fasten the diaper and look at where the tabs land. On a diaper that fits, each tab sits well onto the front panel, evenly on both sides, without touching the other tab. If the pack shows how the tabs should sit, follow that. Watch for these:

  • You are fastening at the very end of the tab, or the tab only just touches the front panel.
  • You have to pull the diaper hard to close it.
  • The waistband puckers at the sides because it is stretched so tight.

Any one of these can be a hint. Two together are a fairly clear sign that the diaper is too small.

Leaks and blowouts that start suddenly

A sudden change in pattern says more than a single leak. If a diaper that held well last week now leaks up the back or around the legs, check the simple causes first:

  1. Was the diaper put on straight and fastened evenly on both sides?
  2. Were the leg ruffles out, not folded in?
  3. Was there a longer gap than usual between changes, or a bigger feed?

If none of those explains it and the leaks keep coming, the size is a likely cause, especially when tight tabs or deep marks show up in the same week.

Marks at the waist and thighs

Look at the skin each time you change the diaper. Deep lines at the waist or around the thighs suggest the elastic is stretched tight, and trying the next size is a simple way to check. If the skin looks sore, rubbed or broken, or a rash is not improving, ask a doctor, nurse or pharmacist. For diaper rash creams, follow the label.

A rise that sits low under the belly button

The rise is the distance from the back waistband, between the legs, to the front waistband. When it is too short for your baby's body, the front sinks below where it used to sit and the back edge rides low. You may notice the waistband slipping down when your baby sits or reaches, or the diaper looking as if it sits on the hips instead of the waist. This sign can turn up together with leaks at the back.

To check, think back to how the same line sat when it fitted well. If the front waistband now sits clearly lower on the belly with the same fastening, the diaper is running short for your baby.

How to switch without wasting the open pack

  1. Wait for two signs, not one, before you change.
  2. Buy a small count of the next size first, and read the count in the product title before you order. The Bambo Nature Diapers, Size 5, 25 Count is a small pack, for example, while the Huggies Snug & Dry Diapers, Size 4, 150 Count is a count to leave until you know the size fits.
  3. Try the new size for a day and see whether the signs go away. Write the date on the pack when you open it, so you can see how long each size lasted when you plan the next one.
  4. If it fits, use it overnight and for outings first, when a leak is most disruptive, and finish the old pack at home during the day for as long as it is not leaking or leaving marks.
  5. Once the old size is clearly tight, stop using it. Leave any unopened pack of the old size sealed, in case someone you know can use it.

You can compare sizes and counts across the Baby Diapers & Training Pants collection.

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Common questions

My baby is inside the weight range but the diaper leaks. Should I move up?

Not on leaks alone. Rule out fastening and timing first, then look for a second sign such as tabs at their limit, deep marks or a low rise. Leaks that come with gaps at the legs point the other way, toward a diaper that is too big.

Can I move up before my baby reaches the next size's weight range?

The range is a guide, so you can try a small pack. Check the larger size for gaps at the legs and waist. If you see gaps, it is still too big, so go back to the smaller size and keep the pack for later.

How often will my baby need a new size?

It depends on how your baby grows, and there is no fixed schedule. A quick look at the tabs, the marks and the rise at one change each week will tell you more than the calendar.

Does a different line change the answer?

Yes. A snug cut can feel small on a baby who fits well in a roomier cut. Try the same size in another line before you assume you must go up.

If you would like a second opinion on a fit problem, send us the size, the line and what you are seeing through the contact page. We reply within one business day.