Baby clothing sizes by age, height and weight

Measure the baby's height, find the row, then check the weight. The age on the label is a shortcut for a typical baby of that age, and babies grow at their own pace, so a tall four-month-old can already be in the next size.

The table is copied from Ruban Size's Baby template, with inches and pounds added (2.54 cm to the inch, 0.4536 kg to the pound). Its note says it in one line: "Choose by height first: age is only a guide." The values are typical, written to be replaced by each brand's own, so the brand's chart wins.

Baby size chart

M stands for months. Height and weight are body measurements: the baby, not the garment. Each row starts where the one before ends: 62 cm is both the top of 0-3 M and the bottom of 3-6 M.

How to read it

1. Measure the height. The template's step: barefoot, back against a wall, from the floor to the top of the head. A baby who doesn't stand yet is measured lying on the back, from the top of the head to the heel, legs gently straightened.
2. Find the row by height, not by age.
3. Check the weight. If it points to the next row, look at the next size too: the weight says something about build that the height doesn't.
4. On the line between two rows, take the larger one. The baby grows into it.

For the measuring itself, with a baby who won't keep still, see how to measure kids for clothes.

Why age is only a guide

The rows are not the same width. In the template, 0-3 M spans 12 cm of height (50 to 62), 3-6 M spans 6 cm, 6-12 M spans 12 cm again, over six months, then 12-18 M and 18-24 M take 6 cm each. Two babies of the same age can sit in different rows, and a narrow row is outgrown sooner than a wide one.

A label with one age, like "3M", doesn't say whether it means up to three months or from three months. A range, as in the template, leaves no doubt, and the height beside it settles the rest.

Newborn sizes, and after 24 months

The template starts at 0-3 M and 50 cm. Some brands sell smaller sizes as well, newborn or preemie. If you do, add those rows with your own heights and weights, and keep the same columns so shoppers can compare.

After 18-24 M come the toddler sizes. In Ruban Size's Toddler template, a 2T has the same height and weight as an 18-24 M (86 to 92 cm, 12 to 14 kg), and the note explains the difference: "T sizes leave room for a diaper." The sizes after that, by age and height up to 14, are in kids' clothing sizes by age and height.

How a Shopify store should show baby sizes

1. The age labels as printed on your garments, with the height and weight of each one beside it.
2. Height first, in the table and in a note: the age alone can point to the wrong row.
3. Both units: centimeters and inches, kilograms and pounds, with a switch.
4. Ranges, not single ages, so 3M can't be read two ways.
5. Separate charts for baby, toddler and kids, each on the right products. Baby clothes and a size 8 dress don't share a chart.

How Ruban Size does it

The Baby template has five rows, 0-3 M to 18-24 M, with the height in centimeters and the weight in kilograms, a How to measure block for the height, and the note about height. Because the chart has a weight row, the unit switch reads Metric and Imperial: one tap turns centimeters into inches and kilograms into pounds. Like every template, it opens as a draft and shows nowhere until you save it and choose its products.

Find my size for kids opens with "Enter your child's measurements. We compare them with this chart." On the Baby template it asks for the height, the weight and the age, in months: the age labels of the chart become an age field of their own. Height counts most; weight and age only check the answer.

A four-month-old of 65 cm and 7 kg gets "Your size: 3-6 M", "Confidence: high". A four-month-old of 70 cm and 8 kg gets "You are between 3-6 M and 6-12 M. We suggest 6-12 M.", with the line "Height 70 cm: 6-12 M, bottom of the range". The age says 3-6 M; the height wins, as the note says it should. When two sizes tie, the larger one is suggested.

The baby's measurements are saved on the shopper's device only, never sent, and kept apart from the parent's own, so "Your size: M" on an adult product doesn't mix with "3-6 M" on a bodysuit. The height and weight here are the chart's own rows, read on every plan. The height and weight estimate of the Fit plan is something else: it is for adults, never for under 18s, and not offered on charts that already have a height row. More on the settings in Find my size.

Questions

What size does a 3 month old baby wear?

It depends on the height. In the template, a baby up to 62 cm is a 0-3 M and a baby of 62 to 68 cm a 3-6 M, so a long three-month-old is already in 3-6 M.

What size should a newborn wear?

In Ruban Size's template, 0-3 M is the first size: 50 to 62 cm (19.7 to 24.4 in) and 3 to 6 kg (6.6 to 13.2 lb). Brands that sell newborn or preemie sizes give them their own, smaller rows.

Is 18-24 months the same as 2T?

The same height and weight in Ruban Size's templates: 86 to 92 cm and 12 to 14 kg. The cut differs: T sizes leave room for a diaper.

Should I buy baby clothes by age or by weight?

By height first, then weight. The Baby template says it plainly: "Choose by height first: age is only a guide."