Diaper size 3: up to what age or weight?

In collaboration with Rokiyah Hosen

Relecture professionnelle

Is your baby still growing fast in the first few weeks of life, and will size 2 diapers soon no longer fit? Are you wondering at what weight your baby can start wearing a size 3 diaper? When should he go up a size?

Everything you need to know about size 3 diapers

Size 3 diapers are for babies weighing between 4 and 9 kg. They can be worn from 3 months up to around 5 or 6 months. After the first three months of life, baby's growth and weight gain tend to slow down.

Size 3 diapers can be worn longer than previous sizes.

When should size 3 diapers be introduced?

As with the previous size changes, there are several signs that will let you know when it's time to move up to the next size. If you notice :

  • Leaks are happening more and more;
  • The absorbent surface is not large enough for your baby's size;
  • The diaper no longer covers the bottom completely;
  • The diaper leaves red marks on your baby's skin, on the thighs and stomach;
  • If it's difficult to close the adhesives and they even tend to peel off.

These are all signs that your baby's diaper is too small and that it's time to move up to the next size.

How many size 3 diapers should I buy for my baby?

As explained above, a size 3 diaper will be used a lot more than a size 1 or 2 diaper. You can therefore carry a larger stock of diapers, without too much risk of not using them.

Depending on your child's weight, you'll need a different number of diapers. Keep an eye on your stock so you don't find yourself without diapers or with too many.

The number of diapers you need will depend on your baby's weight, size and shape! You can refer to our guide below:


1st month (No. of packs of diapers needed)

2nd month (No. of packs of diapers needed)

3rd month (No. of packs of diapers needed)

from 2.5 to 3kg

8 packs Size 1

8 packs Size 1

4 packs size 1, 4 packs size 2

from 3.1 to 3.3kg

8 packs size 1

6 packs size 1, 2 packs size 2

8 packs size 2

from 3.4 to 3.6kg

6 packs size 1, 2 packs size 2

4 packs size 1, 4 packs size 2

8 packs size 2

from 3.7 to 3.9kg

4 packs size 1, 4 packs size 2

8 packs size 2

6 packs size 2, 8 packs size 3

+ over 4kg

1 pack size 1, 7 packs size 2

8 packs size 2

8 packs size 3

How to choose the best size 3 diaper?

Beyond choosing the right size diaper for your baby, you also need to make sure that the diaper you give your baby is healthy for his or her skin. From birth to potty training, your baby will be constantly in diapers.

Your baby's diapers must therefore be perfectly absorbent and harmless.
To achieve this, you need to make sure that your baby ' s diapers contain no toxic chemicals, endocrine disruptors, etc., which could cause irritation, redness, diaper rash or other discomforts for your baby. To do this, you need to know the composition of the different layers of your baby's diaper: the contact layer, the absorbent material, the leak-proof material, the outer material, etc...

You should also have easy access to analysis reports. If they're not available, don't bother - a lack of transparency about product composition is never a good sign.

You should also be wary of false marketing claims or claims that are not based on reliable information. Certain terms, such as hypoallergenic and dermatologically tested , are mandatory for diapers and panty liners.

Instead, refer to the whitening methods. Most diapers today are bleached using the ECF (Elementary Chlorine Free) method, which uses chlorine derivatives that are toxic to baby's skin. Only 5% of baby diapers today are bleached using the TCF (Totally Chlorine Free) method, which uses neither chlorine nor chlorine dioxide.

Several studies have been published by consumer associations and the ANSS, warning of the safety of diaper compositions.

As for the disposable vs. cloth diaper debate, both have their advantages and disadvantages. Cloth diapers are more environmentally friendly, but in terms of cleanliness and risk of irritation, disposable diapers are preferred.

Baby's growing: when to change to a size 4 diaper?

From your baby's 6th month of life, his weight gain continues to slow down. Here are a few signs that should tell you it's time to switch to a size 4 diaper :

  • Leakage is becoming more frequent;
  • It becomes difficult to close the diaper fasteners;
  • Your baby's skin has red marks from the diaper, on his tummy and thighs.

And if you can't close the fasteners at all, don't worry: your baby is growing and it's time to go up a size!