Baby clothes size chart: US sizes from preemie to 24 months

In shortOn the Carter's chart, size NB fits 6 to 9 lb (2.7 to 4 kg) and 18 to 21.5 in (46 to 55 cm), size 3M fits 9 to 12.5 lb (4 to 5.7 kg), and size 24M fits 28 to 30 lb (12.5 to 13.6 kg). We read the number on the label as the end of the age range. By the WHO median curves, a typical girl wears 3M 26 days to 2.8 months and a typical boy 19 days to 2.2 months.

On the Carter's chart, baby sizes go by months: NB, 3M, 6M, 9M, 12M, 18M, and 24M, with the weight and length of each size in pounds and inches and in kilograms and centimeters ¹. Cotokim uses that chart as its reference for US sizes. Below are the chart, the two sizes under NB and how long a typical baby wears each size.

The chart, NB to 24M

Weight and length from the Carter's chart for bodysuits ¹. Its charts for rompers, pajamas and swimwear give the same weight and length for each size from Preemie to 24M ¹.

The weight for each size:

Size	Pounds	Kilograms
NB	6 to 9	2.7 to 4
3M	9 to 12.5	4 to 5.7
6M	12.5 to 17	5.7 to 7.5
9M	17 to 21	7.5 to 9.3
12M	21 to 25	9.3 to 11.1
18M	25 to 28	11.1 to 12.5
24M	28 to 30	12.5 to 13.6

The length for each size:

Size	Inches	Centimeters
NB	18 to 21.5	46 to 55
3M	21.5 to 24	55 to 61
6M	24 to 27	61 to 69
9M	27 to 28.5	69 to 72
12M	28.5 to 30	72 to 76
18M	30 to 32	76 to 81
24M	32 to 34	81 to 86

Under NB, Carter's has two smaller sizes: Preemie, labeled PRE, for up to 6 lb (2.7 kg) and up to 18 in (46 cm), and UP5LB, for up to 5 lb (2.3 kg) and up to 17 in (43 cm) ¹.

How long each size lasts

In the table, the months next to each size are our reading of the label, explained further down. How long your baby wears each size depends on how fast your baby grows. By the WHO median curves of weight ² and length ³, from the day a typical baby reaches the size to the day they pass its top:

Size	A typical girl	A typical boy
NB · newborn	up to 26 days	up to 19 days
3M · 0 to 3 months	26 days to 2.8 months	19 days to 2.2 months
6M · 3 to 6 months	2.8 to 6.7 months	2.2 to 5 months
9M · 6 to 9 months	6.7 to 10.4 months	5 to 9 months
12M · 9 to 12 months	10.4 to 13.7 months	9 to 12.3 months
18M · 12 to 18 months	13.7 to 18.3 months	12.3 to 16.8 months
24M · 18 to 24 months	18.3 to 23.6 months	16.8 to 22 months

A bigger baby (85th percentile) moves up sooner and a smaller one (15th percentile) later: a bigger girl leaves 3M at almost 2 months, and a smaller girl at a little over 4 months ² ³. Cotokim's list uses the same curves, with girls and boys averaged, to split the clothes between sizes ² ³; the first two sizes have a page of their own, which size to start with.

How to read a US size label

Our reading: the number is the end of the age range. Carter's sleep bags use ranges, 0-3M, 3-6M, 6-9M and 9-12M, with the same lengths as its bodysuits in 3M, 6M, 9M and 12M ¹. So we read the number on a bodysuit label as the end of the age range, as in 3M · 0 to 3 months. That reading is Cotokim's.
The smallest size your baby has not outgrown. In the tool below, a baby wears the smallest size whose top length and top weight they have not passed. If length and weight point to different sizes, the tool picks the bigger one, so the clothes are not tight.
On the edge, the smaller size. On the chart, NB goes up to 9 lb (4 kg) and 3M starts at 9 lb (4 kg) ¹. The tool keeps the smaller size until your baby passes the top, a rule of the tool.
Two units, one chart. Carter's lists the sizes in pounds and inches and in kilograms and centimeters ¹. The tool takes pounds and inches.
Brands and products differ. Even at Carter's, the bodysuits in 3M and the sleep bags in 0-3M cover the same lengths and list slightly different weights ¹. For another brand, use that brand's chart, length first and then weight.

Find your baby's size

Pick your baby's age, or type the weight in pounds and the length in inches. The tool shows the likely size, from the same chart, and when the next one usually comes by the WHO median curve:

Likely size at birthNB · newborn18 to 21.5 in (46 to 55 cm) and 6 to 9 lb (2.7 to 4 kg)

Moves up to 3M · 0 to 3 months at 23 days, by the WHO median curve (average of girls and boys).

A bigger baby moves up earlier, at 9 days; a smaller baby moves up later, at a little over 1 month.

Every brand fits differently: when in doubt, compare your baby's length with the brand's chart. The chart here is the official Carter's chart; the window of use of each size comes from the WHO median curve, and a bigger and a smaller baby are the 85th and 15th percentiles.

For a premature or small baby, Carter's also has UP5LB: up to 5 lb (2.3 kg) and PRE: up to 6 lb (2.7 kg).

Cotokim's list counts how many pieces of each size to have, from your due date and your city's climate.

Build my list for my city

This chart is for choosing clothes: on this page, the WHO curves only estimate how long each size lasts. How your baby is growing is a question for your baby's health care team, who have the most up-to-date information on growth and development ⁴. For a premature or sick baby, follow your baby's care team ⁴. The months next to each size and the edge rule of the tool are Cotokim's. Checked by the Cotokim team against the sources on this page. It does not replace advice from the health care team that looks after you and your baby.

Frequently asked questions

What size is a newborn in US baby clothes?

Size NB, for 6 to 9 lb (2.7 to 4 kg) and 18 to 21.5 in (46 to 55 cm) on the Carter's chart ¹. By the WHO median curves, a typical girl wears it up to 26 days and a typical boy up to 19 days ², so our suggestion is a few NB pieces and most of the first clothes in 3M.

Is 3M the same as 0-3 months?

That is how we read it. On the Carter's chart, bodysuits in 3M cover the same lengths as sleep bags in 0-3M ¹, so the number is the end of the age range. By the WHO median curves, a typical girl wears 3M 26 days to 2.8 months and a typical boy 19 days to 2.2 months ².

Should I go by weight or by length?

By both. The tool picks the smallest size your baby has not outgrown in length and in weight, and the bigger one when the two disagree. With another brand's chart, check the length first and then the weight.

What size for a premature baby?

Carter's has Preemie, for up to 6 lb (2.7 kg), and UP5LB, for up to 5 lb (2.3 kg) ¹. Cotokim's list does not count these sizes, because a typical newborn is born bigger, on the WHO median weight curve ². For a premature baby, follow your baby's care team ⁴.

Do all brands fit the same?

Not always. Even at Carter's, the bodysuits in 3M and the sleep bags in 0-3M cover the same lengths and list slightly different weights ¹. For another brand, use that brand's chart.

Source credits

Courtesy: Eunice Kennedy Shriver National Institute of Child Health and Human Development. Safe to Sleep® is a registered trademark of the U.S. Department of Health and Human Services.

Brands appear only for the charts of their own products (sizes, packs, TOG). Cotokim has no deal with any brand.

Written by the Cotokim teamChecked by the Cotokim team against the sources on this page, on October 15, 2026

Sources

Carter's, Kids Clothing Size Chart. Read on October 14, 2026.
World Health Organization, WHO Child Growth Standards: weight-for-age. Read on October 11, 2026.
World Health Organization, WHO Child Growth Standards: length/height-for-age. Read on October 11, 2026.
Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), NIH, Ways to Reduce Baby's Risk (Safe to Sleep). Read on October 14, 2026.