How to measure a baby for clothes

Baby clothes are cut for a length and a weight. The months on the label assume a typical baby of that age, and babies of the same age can be a size apart. Ruban Size's Baby template prints the rule under its table: "Choose by height first: age is only a guide." On baby charts, height means the baby's length, measured lying down.

What you need

A soft tape measure, a firm flat surface with a wall or a headboard at one end (a changing mat on the floor works), two hardback books, and a second person. For the weight, a bathroom scale.

How to measure a baby's length

Lay the baby on their back on the firm surface, the top of the head touching the wall, or a book stood on end against it.
Keep the head straight. Your helper holds it gently, the baby looking straight up, chin neither tucked nor raised.
Straighten the legs gently, one hand resting on the knees. Babies curl up, and a curled baby measures short.
Feet flat against a book. Toes pointing up, stand the second book against the soles, upright.
Mark where the book stands, then lift the baby away.
Measure from the wall to the mark. Write it down with the unit and the date.

On a bed or a changing table, keep one hand on the baby the whole time. If the baby fights the tape, try again after a feed or during a nap: a quick reading of a calm baby beats a careful one of an upset one.

How to weigh a baby at home

Weigh yourself, then weigh yourself holding the baby, and subtract. Do it with the baby in a dry diaper and light clothes. The weight from the latest check-up works too, if it's recent.

Other measurements worth taking

Head, around the widest part, just above the eyebrows and ears, the way the hat measuring guide does it. For hats, and for tops that pull over the head. The Kids' hats template gives 40 to 43 cm for 0-6 M, 44 to 46 cm for 6-12 M and 47 to 49 cm for 1-2 Y.
Chest, under the arms, tape level, for knitwear.
Foot length, heel to the tip of the longest toe, for socks and booties.

Baby sizes in the Baby template

The Baby template runs from newborn to two years, by length and weight. Inches and pounds are added here (2.54 cm to the inch, 2.2046 lb to the kilogram):

Age	Height (cm)	Height (in)	Weight (kg)	Weight (lb)
0-3 M	50-62	19.7-24.4	3-6	6.6-13.2
3-6 M	62-68	24.4-26.8	6-8	13.2-17.6
6-12 M	68-80	26.8-31.5	8-10	17.6-22
12-18 M	80-86	31.5-33.9	10-12	22-26.5
18-24 M	86-92	33.9-36.2	12-14	26.5-30.9

These are typical values; a store puts in its own. After 18-24 M come the toddler sizes, 2T to 5T, with room for a diaper; how to measure kids for clothes takes it from there, and every age side by side is in kids' clothing sizes by age and height.

Common mistakes

Measuring a curled-up baby. Bent knees take centimeters off.
Buying by age alone. A long four-month-old can be past the 3-6 M length already.
Old numbers. Babies grow fast; measure again before buying ahead.
Forgetting the diaper. Bodysuits and sleepsuits go over it, and a full one takes room.
The exact size for something meant to last a season. Between two sizes, the larger one lasts longer.

What it means for a Shopify store

Parents and gift buyers shop differently. Parents can measure; gift buyers often know only the age. A good baby chart serves both:

Length and weight next to every age, in both units.
Which comes first, in a line under the table, like the template's "Choose by height first: age is only a guide."
A measuring step written for babies. The template's step is the standing one: "barefoot, back against a wall, from the floor to the top of the head." For newborn and infant sizes, rewrite it in the editor, for example "Length: lying on their back, from the top of the head to the heel, legs straight." Keep the step linked to the height row so it lights up with it.
Diaper room and stretch, if your cuts allow for them.

How Ruban Size handles baby sizes

On a baby chart, Find my size speaks to the parent: "Enter your child's measurements. We compare them with this chart." It asks for what the chart has, here height and weight, and adds an Age field in months, because the sizes ("0-3 M", "6-12 M") are ages.

The height counts most. The weight and the age are hints that only nudge the answer, and close calls go to the larger size, which leaves room to grow. A baby of 74 cm and 9 kg gets "Your size: 6-12 M". A four-month-old of 69 cm and 7.5 kg reads "You are between 3-6 M and 6-12 M. We suggest 6-12 M.", with "Height 69 cm: 6-12 M, bottom of the range", the weight and the age both "below this size's range", and "3-6 M may also fit if you like a closer fit." By age alone, that baby would get 3-6 M, already outgrown.

A child's measurements are saved on the parent's device apart from the parent's own, and never sent. A parent's chest never fills a child's form. The height and weight estimate of the Fit plan isn't offered for children. Kids sit with rings, shoes, bras and dogs in fit by product type, each with its own questions.

The real size guide: Baby size chart. Switch units, or open Find my size.

Age	Height (cm)	Weight (kg)
0-3 M	50-62	3-6
3-6 M	62-68	6-8
6-12 M	68-80	8-10
12-18 M	80-86	10-12
18-24 M	86-92	12-14

How to measure

Height: barefoot, back against a wall, from the floor to the top of the head.

Choose by height first: age is only a guide.

Questions

How do you measure a baby's length?

Lay the baby on their back on a firm surface, head against a wall, and gently straighten the legs. Stand a book against the soles, mark where it stands, and measure from the wall to the mark.

Should I buy baby clothes by age or by weight?

By length first, then weight. The age on the label assumes a typical baby, and a long or heavy baby can need the next size months early.

What does 6-12 M mean on baby clothes?

A size cut for babies of about 6 to 12 months. On the Ruban Size Baby template, it covers a length of 68 to 80 cm and a weight of 8 to 10 kg.

How often should I measure my baby for clothes?

Before each purchase, or at least each season. Babies outgrow sizes within weeks, and last month's numbers are already short.