Baby pyjama sizes explained: newborn to 5 years

Baby pyjama sizes can look confusing when one label says 0–3 months and another says 62 cm. This guide explains how those labels usually work from newborn to around 5 years, how to measure, and how to dress a baby safely for sleep, with guidance from the NHS and The Lullaby Trust. You will find current sleepsuits and rompers in our baby clothes and baby pyjamas collections.

How baby pyjama sizes are labelled in the UK and EU

In the UK, baby and toddler sleepwear is often labelled by age, such as newborn or 0–3 months. In the EU, the same garments are often labelled by height in centimetres. Many product pages, including ours, show both. A typical example on a House of Zuza romper is “0–3 months / 50–62 cm”.

These bands are a starting point. Babies of the same age can differ in length, so measure your child and compare the height with the product size guide. If they are close to the top of a band, sizing up is often more comfortable for daytime clothes. For a sleeping bag, The Lullaby Trust notes that most bags are fitted by weight, not age, so follow the maker’s guide. Many UK and European labels use height bands in this pattern, but shops do vary:

Common UK age label	Often matched with EU height
Newborn	50–56 cm
0–3 months	50–62 cm
3–6 months	62–68 cm
6–9 months	68–74 cm
9–12 months	74–80 cm
12–18 months	80–86 cm
18–24 months	86–92 cm
2–3 years	92–98 cm
3–4 years	98–104 cm
4–5 years	104–110 cm

Prefer the measurements on the item you are buying, including any centimetre range shown next to the age label.

Three cotton baby rompers in pink, yellow and blue with simple animal and star prints and popper fastenings down the legs — The pure cotton long-sleeve romper has poppers at the leg and is listed from 0–3 months to 12–18 months.

How to measure and when to size up

Lie a baby down and measure from the top of the head to the heel. For a toddler who can stand, measure against a wall, without shoes. Check that the chest is not tight and that you can change a nappy easily. Poppers or a zip along the legs are simpler at night than a style you pull over the head. Sleepwear should not be baggy enough to ride up over the face, or so tight that it presses on the chest. If it is short in the body or feet, move up a size. If you use a baby sleeping bag, The Lullaby Trust advises choosing one that fits well around the neck and shoulders, so the baby cannot wriggle down inside, and following the weight and tog guide.

Cream long-sleeve baby romper with a red heart print, front poppers from neck to foot, and a nappy-change opening at the leg — Front poppers, as on this long-sleeve bodysuit romper, make night changes easier. Sizes run from 0–3 months to 9–12 months.

Safer sleep tips when you dress a baby for bed

Safer sleep advice from the NHS and The Lullaby Trust applies for every sleep, day and night, in the first year (and for longer if your baby was premature, following their guidance).

The NHS says the safest place for a baby to sleep for the first six months is on their back, in their own cot or Moses basket, in the same room as you. Use a firm, flat mattress and keep the cot clear of pillows, duvets, cot bumpers, loose bedding, soft toys, pods and nests. If you use a light blanket, the NHS and Lullaby Trust describe the feet-to-foot position: feet at the bottom of the cot, blanket tucked in no higher than the shoulders.

The NHS and The Lullaby Trust recommend trying to keep the room at 16–20°C, and say that babies who get too hot are at higher risk of sudden infant death syndrome (SIDS). Feel the baby’s chest or the back of the neck, not their hands or feet. If their skin is hot or sweaty, remove a layer.

The Lullaby Trust’s guidance on how to dress your baby for sleep is practical: in a room of 16–20°C, a baby grow with a lightweight, well-fitting sleep bag, or a firmly tucked lightweight blanket, is a common combination. In hotter conditions, a short-sleeve bodysuit, or even just a nappy, can be enough. Hats and hoods should come off indoors, because babies lose heat through their heads. Do not add a blanket on top of a sleeping bag, or use two bags together. Weighted bedding is not recommended for babies under one year.

Short-sleeve baby rompers in white, blue, yellow, grey, green and pink, made from a light textured fabric with button fronts, laid flat — A light, short-sleeve layer, such as the breathable mesh short-sleeve romper, can work in a warmer room. Check your baby’s chest or neck, as the NHS and Lullaby Trust advise, rather than guessing from the weather alone.

Read the NHS pages on safer sleep and SIDS, and The Lullaby Trust’s safer sleep overview. Shop baby clothes and baby pyjamas.

FAQs

Should I go by age or by height?

Height is usually more useful, because babies grow at different rates. Use the age label as a rough clue, then check the centimetre range and the product size guide.

Can my baby wear a hat or a hood in their cot?

No. The Lullaby Trust says hats should be removed indoors, and hoods should come off for sleep, so the baby can lose heat through their head.

Is a thicker sleepsuit safer in winter?

Not automatically. Add or remove layers after you feel the baby’s chest or neck, and keep the room around 16–20°C where you can, as the NHS and Lullaby Trust advise.

What if the size is wrong?

UK and EU customers have 14 days to change their mind on most unused items, starting the day after delivery. Email hello@houseofzuza.com for the return address. You pay the return postage.