Diaper Size Age Weight
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2 Four to seven months 12 to 18 pounds
3 Seven to 12 months 16 to 28 pounds
4 18 to 48 months 22 to 37 pounds
5 Three years and up 27 pounds and up
Try the next size up in diapers to see if it absorbs better and fits your baby more comfortably. If leaks stop and it looks like a better fit, your baby was most likely ready to move up. If you notice excessive gapping at the legs and waist, the diaper may be too large for your baby.Jan 7, 2016
What size diapers is a 4 month old in?
Diaper Size Age Weight
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1 2-4 months 8-14 lbs (4-6 kg)
2 4-7 months 12-18 lbs (5-8 kg)
3 7-20 months 16-28 lbs (7-13 kg)
4 18-48 months 22-37 lbs (9-17 kg)