Costs for Littles logo

Diaper calculator

How many diapers will you need?

Enter your baby's growth curve and dates, and get a size-by-size plan for disposable diapers.

Skip to the calculator

First, how weight maps to diaper sizes

Here's the typical growth curve climbing through the size bands from birth to age 2.

Diaper size bands by weight and age

Typical growth for boys and girls; each shaded band is a diaper size

boys girls
Chart of typical baby weight from birth to 24 months, overlaid on diaper size weight bands from Preemie through Size 7. The median baby moves quickly through Newborn, Size 1 and Size 2 in the first five months, then spends most of the first two years in Sizes 3 to 5, weighing roughly 7 pounds at birth and 25 to 27 pounds by age 2.
A typical baby is born around 7 lb, starting with Newborn diapers, moves through Sizes 1 and 2 in the first five months, enters Size 3 near 6 months, and then spends most of the first two years in Sizes 3 to 5, reaching roughly 25–27 lb by age 2.

The growth curves show the median weight for boys and girls, from the WHO Child Growth Standards via the CDC ↗. The diaper size bands are generic estimates. Real ranges vary by brand and overlap, so a baby often fits two sizes at once, and the box will list your brand's exact range. A planning guide, not medical advice. Your pediatrician tracks your baby's actual curve.

Build your plan ↓

Build your diaper plan

Set your baby's weight and dates below, and we'll do the math. Adjust anything to match your reality.

Your details updating…

1 Your baby ▾
Sex (for the growth curve)
Growth curve (for sizing)
2 Your dates ▾

Default is your baby's first two years.

3 Usage (optional, defaults if skipped) ▾

We taper between these as your baby ages, then hold steady. Adjust to match your reality.

When size ranges overlap, you usually

Ranges overlap, so a 13 lb baby fits both Size 1 and Size 2. Pick whichever matches how you like to size.

Covers real life: blowout double-changes, daycare stashes, crazy days, travel, etc.

Estimate covers standard diapers only.

4 Costs (optional, defaults if skipped) ▾
$0.15$0.50

Other sizes scale automatically (smaller sizes cost less per diaper, bigger ones more). Want your real number? Find your cost per diaper below ↓ then set it here.

5 Size chart (optional, defaults if skipped) ▾

Generic defaults in lb; edit to match your preferred brand. Leave the top weight blank for open-ended sizes.

Preemie to lb
Newborn to lb
Size 1 to lb
Size 2 to lb
Size 3 to lb
Size 4 to lb
Size 5 to lb
Size 6 to lb
Size 7 to lb

Click Calculate to see your plan estimates after making changes. Planning tool only.

Your plan shows up here

Pick your baby's sex, set the details, and hit Calculate.

Find your real cost per diaper

Diaper math is sneaky: the giant box might not be the best deal once coupons and promos land. Compare your real options here. The starter rows show common deals; edit them in place.

Brand Store Size Packs Diaper Count Price ($) Coupon Cost / diaper Notes

Diaper calculator FAQ

How many diapers will I need in the first year?

Most babies go through roughly 2,500 to 3,000 diapers in year one, starting around 10 to 12 changes a day as a newborn and easing toward 6 a day by the first birthday. This calculator projects your own total by size using your baby's growth curve and dates.

What size diapers will my baby wear, and when?

Diaper size follows weight, not age. This tool uses the WHO weight-for-age growth standards for your baby's sex and percentile (or a current weight you enter) to project which size fits each week, and when to expect each size change.

How many diapers per day by age?

Newborns typically need about 10 to 12 changes a day, easing to around 6 a day by age one as feeding and sleep settle. The drop is steepest in the first few months and then flattens out, so around six months most babies sit near 7 a day rather than halfway between the two. You can adjust both the newborn and one-year rates to match your baby.

How many boxes of each size should I buy?

Babies pass through the smallest sizes quickly, so buy those sparingly and stock up on the long-haul sizes like 3 and 4. Turn on the boxes option to convert the estimate into boxes per size, accounting for the fact that bigger sizes come fewer to a box.

Is this diaper calculator medical advice?

No. It is an independent planning and budgeting estimate for standard diapers, not medical advice, and it does not store what you enter. Babies grow at their own pace, so treat the sizes and counts as a planning guide.