Baby Clothes Size Calculator
Find baby clothing size from age, weight, and height.
Returns US, UK, and EU sizes for newborn through 24 months with brand size comparison.
Baby clothing sizes vary by brand and region, but are generally based on weight and height/length.
US Baby Clothing Sizes:
| Size | Age | Weight | Height | EU | UK |
|---|---|---|---|---|---|
| Preemie | Premature | Up to 5 lbs (2.3 kg) | Up to 17 in (43 cm) | 44 | Tiny Baby |
| Newborn | 0–1 months | 5–8 lbs (2.3–3.6 kg) | 17–21 in (43–53 cm) | 50-56 | Newborn |
| 0–3M | 0–3 months | 8–12 lbs (3.6–5.4 kg) | 21–24 in (53–61 cm) | 56-62 | Up to 3 months |
| 3–6M | 3–6 months | 12–16 lbs (5.4–7.3 kg) | 24–27 in (61–69 cm) | 62-68 | 3-6 months |
| 6–9M | 6–9 months | 16–20 lbs (7.3–9.1 kg) | 27–29 in (69–74 cm) | 68-74 | 6-9 months |
| 9–12M | 9–12 months | 20–24 lbs (9.1–10.9 kg) | 29–31 in (74–79 cm) | 74-80 | 9-12 months |
| 12–18M | 12–18 months | 24–28 lbs (10.9–12.7 kg) | 31–33 in (79–84 cm) | 80-86 | 12-18 months |
| 18–24M | 18–24 months | 28–30 lbs (12.7–13.6 kg) | 33–35 in (84–89 cm) | 86-92 | 18-24 months |
| 2T | 2 years | 30–33 lbs (13.6–15 kg) | 35–37 in (89–94 cm) | 92-98 | 2-3 years |
The weight and height columns overlap on purpose, and the top of one row is the bottom of the next. A baby who measures exactly 12 lbs is at the end of 0–3M and the start of 3–6M, so the calculator gives the larger of the two.
Metric conversions:
- Weight:
kg = lbs × 0.453592 - Height:
cm = inches × 2.54
Tips:
- When between sizes, always size up
- Different brands run small or large, so check each brand’s own chart
- Consider the season ahead when buying clothes for growing babies
Why the same baby wears two different sizes
There is no standards body behind any of this. The number on the label is a manufacturer’s opinion, not a measurement. Carter’s tracks the chart above fairly closely. Gap and Old Navy tend to run generous, so a baby who measures 3-6M often fits their 0-3M. European labels such as H&M size by height in centimeters and cut narrower through the hips, which catches out parents of cloth-diapered babies.
Weight is the better guide for the first year, and length takes over after that. A chunky four-month-old and a long, lean nine-month-old can land in the same size for completely different reasons. When the two answers disagree, take the larger one. Sleeves that are too long roll up; sleeves that are too short are just finished.
One practical note on footed sleepers: they run out of length before anything else does. A cramped foot is the usual reason a sleeper gets retired while the body still fits fine.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.