Which size is my baby?
- Carter's Newborn
- Gerber 0-3M
Weight is the main guide; length matters too. If snaps strain or feet are cramped, go up a size.
The short answer
- Newborn (NB) is the smallest regular size, for babies up to about 8 or 9 lb depending on the brand.
- 0-3M is a range label used by many brands, for roughly 8 to 12 lb.
- 3M is Carter's single-size label for the same stage. Carter's says its 3M "typically compares to the 0-3M range in other brands." Source: Carter's guide to size labels.
Age on the label is only a starting point. Carter's says sizes are typically based on weight and length, and not every 3-month-old will fit the 3-month size.
Two brands, side by side
Carter's
| Preemie | Up to 6 lb |
|---|---|
| Newborn | 6–9 lb |
| 3M | 9–12.5 lb |
| 6M | 12.5–17 lb |
| 9M | 17–21 lb |
Gerber Childrenswear
| Preemie | Up to 5 lb |
|---|---|
| Newborn | 5–8 lb |
| 0-3M | 8–12 lb |
| 3-6M | 12–16 lb |
| 6-9M | 16–20 lb |
From each brand's size chart, checked October 12, 2026: Carter's size chart, Gerber Childrenswear size chart. Notice that an 8½ lb baby is Newborn at Carter's but 0-3M at Gerber.
How long does Newborn size last?
Not long. For a baby born at the average weight, our growth estimate (WHO standards, via the CDC) puts Carter's Newborn size at about birth to 3 weeks, and 3M at about 3 weeks to 2 months. A baby born at 9 lb or more may skip Newborn size completely.
What to buy before birth
- A few pieces in Newborn, enough for the first days, in case your baby is small.
- Most of your first set in 0-3M (or Carter's 3M), since nearly every baby wears it for weeks.
- Leave tags on and keep receipts, so you can swap sizes once you know.
How many of each, by the season your baby arrives and your laundry routine, is worked out in the onesies and sleepers calculator.
Recall check: on October 12, 2026 we searched new CPSC recalls since September 12, 2026 for Carter's and Gerber: none found. We check every month. How we check.
Sizes and safety
For sleep, the AAP says dress your baby in only one layer more than you're wearing, and keep loose blankets out of the sleep space. See the nursery safe sleep checklist. In the car, thin layers go under the harness and a blanket goes over it, never a puffy coat underneath.