Premature baby clothing size guide
Simple rule of thumb for choosing between sizes
- If baby is near the top of a bracket or is long, go up.
- If baby is near the bottom or looks swamped in the limbs, go down.
- If baby has lines/leads or you want easier changing, err slightly bigger for access and comfort.
If in doubt see the Product Details section for each item to see measurements or contact us.
Why are clothing size brackets quite wide?
Premature baby clothing sizes use wider weight brackets because weight alone isn’t a precise predictor of body shape, and premature babies grow fast and unevenly in the early weeks.
It's important to remember that a 4lb baby isn't half the size of an 8lb baby for example.
- Babies carry weight differently. Two babies who both weigh 4lb can have very different proportions (length, torso, leg length, head size), especially if one is early-preterm and one is growth-restricted but closer to term.
- Gestational age matters as much as weight. A 32-week baby and a 36-week baby might weigh the same, but their body composition and proportions can differ a lot.
- Growth is rapid. In NICU and the first weeks at home, babies can move through sizes quickly. Wider ranges mean the garment still fits comfortably through a growth spurt instead of becoming obsolete in days.
- Clothing needs to accommodate medical care. Preterm garments often allow room for nappies, monitors, leads, lines, and easier access for checks. That “extra” can make the fit feel a bit broader by design.
- Manufacturing practicality. Making very narrow size increments would create lots of near-identical SKUs, higher costs, and worse availability—especially for the smallest sizes.
If in doubt see the Product Details section for each item to see measurements or contact us.
Why it’s OK (and often better)
- Better longevity: A 3lb–5lb item can fit well at 3lb and still be wearable as baby approaches 5lb, so you get more use out of each piece.
- Comfort over “perfect tailoring”: For premature babies, softness, ease of dressing, and non-restrictive fit matters more than a super precise size.
- Layering helps: Prem babies are usually dressed in layers (vest + sleepsuit + cardigan/blanket as advised). Slight flexibility in fit is normal and safe.
- You can fit by length and proportions: If a baby is long for their weight, you may size up; if they’re petite/short, you may stay in the lower bracket even if they’re near the top weight-wise.
If in doubt see the Product Details section for each item to see measurements or contact us.
Example of sizing difference
It's important to remember that a 4lb baby isn't half the size of an 8lb baby for example.
These are the measurements of this very well sized bodysuit. As you will see the difference in size is surprisingly small considering the range of 3lb to 7lb.
3-5lb
• Side to side: 15cm
• Shoulder to crotch: 25cm
• Shoulder to wrist cuff: 12cm
4-7lb
• Side to side: 18cm
• Shoulder to crotch: 30cm
• Shoulder to wrist cuff: 17cm
If in doubt see the Product Details section for each item to see measurements or contact us.
