Baby Clothing Sizes: What the Labels Mean and How to Use Them
There is a specific moment most new parents encounter: standing in front of a rack of baby clothing, holding something labelled 0000 in one hand and 000 in the other, with no clear sense of which one their baby will actually fit. The labels count down instead of up, the age ranges printed on the tags do not account for the fact that babies grow at wildly different rates, and buying the wrong size means either a garment that is never worn or one that is outgrown before it has been washed twice.
This guide breaks down how the Australian baby sizing system works, how long each size typically lasts, and how a newborn essentials set plus two everyday bodysuits from Lūmmi in Colour fit into different stages of a baby’s wardrobe.
The Australian Baby Sizing System
Australian baby clothing sizes range from 0000 (the smallest) through to size 1, with the numbers reading in the opposite direction to what most adults expect. Here is the full range:
| Size | Age Guide | Notes |
| 0000 | Newborn, 0–3 weeks | Often the shortest window; larger babies may skip it |
| 000 | 0–3 months | Most-used early size; the reliable starting point |
| 00 | 3–6 months | Fast growth phase; babies can move through this quickly |
| 0 | 6–12 months | More movement, more room needed in the body and shoulders |
| 1 | 12–18 months | Early walking stage; fit varies more across styles |
Two things worth knowing before buying:
- Birth weight often shapes whether 0000 is useful — but only as a rule of thumb, not a medical guideline. Many parents find that a baby born at about 3.5 kg or above may fit 000 from the start and skip 0000 entirely — yet every baby differs. If you are buying before the birth, one or two 0000 items is usually enough just in case. Buying too many pieces in this size is rarely worthwhile.
- Length drives fit more than weight. A baby on the longer side will move out of each size faster through the torso and leg length, even if the weight is still in range. When in doubt, Lūmmi in Colour’s own advice is to size up — all their garments are regular fit and true to size, so a little extra room is more comfortable than a fit that pulls at the neck or snaps.
It is also worth knowing that the Lūmmi in Colour size guide lists garment measurements in centimetres by size — for example chest width and total garment length — which is often more reliable than going by the age band on the hang tag alone. Comparing those measurements against a piece that already fits — or checking garment length against your baby’s body — is usually more reliable than relying on weight alone, particularly once babies move beyond the first few weeks and growth becomes less predictable week to week.
How Long Each Size Actually Lasts
This is the question most sizing guides sidestep. The honest answer is that it depends, but the pattern holds well enough to plan around:
On average, 0000 lasts about two to four weeks for a typical-sized baby, and sometimes less. It is the most over-purchased size in the newborn stage. One full outfit and a spare is a reasonable quantity.
000 is the size most babies spend the longest in during the early months.For many babies, that is roughly six to ten weeks in 000 — and it is the stage where having enough pieces in rotation matters most. Bodysuits in particular get washed daily — three or four in the same size is not excessive.
From 00 through size 1, each size window often lasts roughly three to six months, slowing down as the baby gets older. Growth that felt rapid in the early weeks tends to settle, and the gaps between size changes stretch out from here.
Most parents end up needing far fewer 0000 pieces than they expected, and far more in 000.
What to Buy at Each Stage
The Newborn Stage: Start Compact
For 0000 and 000, the goal is to have a complete set without buying more than the stage requires. The Organic Cotton 6PC Essentials Set — Heather Sage Green is designed specifically for this window — it only comes in 0000 and 000:
- 1x long sleeve bodysuit
- 1x zip-footed growsuit
- 1x singlet bodysuit
- 1x footed leggings
- 1x knotted beanie
- 1x rounded bib with dual snap fasteners
- 1x drawstring bag
Lūmmi in Colour Organic Cotton 6PC Essentials Set in heather sage green, flat lay.
What makes a bundled set useful is the convenience as much as the price — you are not building an outfit from separate pieces at a stage when most parents have limited time and decision fatigue is real. Everything is made from 100% organic cotton in the same heather sage green. The muted earthy tone photographs naturally and works just as well for trips home from hospital as it does for everyday wear at home.
The included drawstring bag also keeps everything together for gifting or hospital packing.
Practical sizing tip: many parents choose 0000 if they are expecting a smaller newborn, and go straight to 000 if they would prefer a little more room and a longer period of wear.
000Through Size 1: The Pieces Worth Buying Across Multiple Sizes
Once you move past the newborn stage, the question shifts from “what to buy for right now” to “which pieces are worth buying again as the size changes.” Two bodysuits stand out here for different reasons.
For cooler months: The Organic Cotton Waffle Long Sleeve Bodysuit — Dusk Blue runs the full range from 0000 to size 1. The waffle knit is suited to spring, autumn, and winter — it adds warmth without adding bulk, and the texture keeps its shape well after repeated washing in a way that plain jersey often does not. With a button placket at the neckline and snap closures at the bottom, it is straightforward to put on and to manage a nappy change without fully undressing the baby. The dusk blue tone feels muted rather than overly bright, which makes it easy to layer across seasons.
Baby wearing Lūmmi in Colour Organic Cotton Waffle Bodysuit in dusk blue on a bed.
For everyday wear: The Organic Cotton Long Sleeve Bodysuit — Chenille Bear is a white 100% organic cotton bodysuit with a raised chenille bear on the chest. White is a practical wardrobe choice across sizes — it pairs with everything, goes under overalls, and looks clean in photos. The chenille detail gives it enough character to work on its own without needing to build an outfit around it. The envelope neckline is worth noting for sizing purposes: it stretches for easy over-the-head dressing, which makes it more forgiving when a baby is between sizes than a standard button-placket collar. Like the waffle bodysuit, it runs from 0000 through to size 1.
Baby wearing Lūmmi in Colour Organic Cotton Long Sleeve Bodysuit — Chenille Bear, on a blanket.
A useful approach with both: buy one in the current size and one in the next size up when restocking. You will almost always need the next size sooner than expected.
Final Takeaway
The Australian baby size system is straightforward once the counting direction clicks. Once you understand how quickly babies move through sizes, buying ahead becomes much easier — and helps avoid ending up with unworn clothes in the drawer.
Common FAQs
What does 0000 mean in Australian baby clothing?
It is the smallest standard newborn size, for the first 0–3 weeks of life. The system counts down rather than up — 0000 is smaller than 000, which is smaller than 00, and so on through to size 1.
Should I size up when buying baby clothes?
In most cases, yes. Slightly oversized baby clothes are more comfortable than clothes that feel too tight, particularly around the neckline or snap closures. All Lūmmi in Colour garments are regular fit and true to size, so sizing up usually just gives a little extra room rather than changing the overall fit dramatically.
Is it worth buying baby clothing ahead in the next size up?
For staple pieces like bodysuits, yes — especially approaching a season change. For occasion items or prints, buying ahead is riskier as fit varies more between styles.
How do I know when my baby has outgrown a size?
Watch the snap closures first: if they pull or no longer lie flat, it is time to move up. Footed items like the growsuit in the 6PC set will show it at the feet before the rest of the body feels tight.
What size should I buy as a baby shower gift?
For baby-shower gifts, many people skip 0000 unless the baby is expected to be very small — 000 fits most newborns from birth and is the most-used early size. For a more generous window, 00 (3–6 months) is a safe choice that will still be relevant once the baby arrives.
