Diaper Size & Quantity Calculator
Enter your baby's weight and age to see the diaper size that likely fits and roughly how many you'll use a day and a month.
Stock up without over-buying
Diapers are the steady drumbeat of the first year — thousands of them. Knowing your baby's likely size and monthly count helps you buy the right boxes, compare cost-per-diaper across pack sizes, and avoid a closet full of a size they've already outgrown.
Fold the monthly count into your budget with the First-Year Baby Cost Estimator, and check your baby's weight trend with the Baby Growth Percentile Calculator.
Frequently Asked Questions
How are diaper sizes decided?
Diaper sizes are set mainly by weight, not age. Newborn covers roughly up to 10 lb (4.5 kg), Size 1 to about 14 lb, Size 2 to 18 lb, Size 3 to 28 lb, and up from there. The ranges overlap on purpose and vary a little by brand, so two babies of the same age can wear different sizes.
How many diapers a day will I actually use?
A lot at first. Newborns often go through 10–12 a day because they feed and fill so frequently; that eases to around 8–9 in the first few months and 6–7 in the second half of the first year. This calculator uses your baby's age to estimate the daily count and multiplies it out to a monthly total for stocking up.
When should I size up?
Let fit lead, not the number on the box. Move up a size when the diaper leaves red marks at the waist or thighs, when you can't fully close the tabs, when leaks and blowouts become frequent, or when the tabs are reaching the edges. Many parents size up just before overnight to get more absorbency for long stretches.
How many should I buy before the baby arrives?
Don't over-stock the smallest sizes — babies grow through Newborn and Size 1 fast, and some skip Newborn entirely. A common approach is one modest pack of Newborn plus a couple of packs of Size 1, then buy larger sizes as you go. Keep receipts so you can exchange unopened boxes for the next size up.
Informational estimate only — brand sizing and your baby's build vary, so use fit as the real guide.