Baby & Infant Size Converter
By KAMP Inc. / UnitOwl · Last reviewed:
Convert baby weight between pounds + ounces, kilograms, and grams. Look up clothing and shoe sizes across US, UK, and EU systems.
Average Baby Weight by Age
| Age | Boys (kg) | Girls (kg) | Boys (lbs) | Girls (lbs) |
|---|---|---|---|---|
| Birth | 3.3 | 3.2 | 7.3 | 7.1 |
| 1 month | 4.5 | 4.2 | 9.9 | 9.3 |
| 3 months | 6.4 | 5.8 | 14.1 | 12.8 |
| 6 months | 7.9 | 7.3 | 17.4 | 16.1 |
| 9 months | 9.2 | 8.6 | 20.3 | 19.0 |
| 12 months | 10.0 | 9.2 | 22.0 | 20.3 |
Understanding Baby Weight Milestones
In the United States, pediatricians typically report baby weight in pounds and ounces (e.g., "7 lbs 8 oz"), while most other countries use kilograms and grams. This difference can be confusing for parents comparing growth charts, especially when consulting international resources or communicating with family abroad.
The average full-term newborn weighs approximately 7.5 pounds (3.4 kg). Most healthy newborns fall between 5.5 and 10 pounds (2.5 to 4.5 kg). Babies typically lose 5-7% of their birth weight in the first few days of life, then regain it by about 10-14 days old. After that, expect roughly 5-7 ounces (150-200 grams) of weight gain per week during the first few months.
By 5 months, most babies have doubled their birth weight, and by 12 months, they've roughly tripled it. Your pediatrician tracks your baby's growth on WHO or CDC percentile charts — these charts use metric units (kg), so knowing how to convert between systems helps you follow along.
Baby Clothing Size Tips
Baby clothing sizes are notoriously inconsistent between brands. The age ranges printed on labels (e.g., "3-6 months") are approximate guides, not exact fits. The most reliable way to choose the right size is to measure your baby's height in centimeters and match it to the manufacturer's size chart.
EU baby clothing sizes are actually based on the child's height in centimeters, making them more precise than age-based US and UK sizes. For example, EU size "68" is designed for a baby approximately 68 cm tall, regardless of their age.
Pro tip: When buying gifts or stocking up, always size up rather than down. Babies grow quickly, and slightly large clothes are still wearable, while too-small items may never be worn. For newborn gifts, skip the "newborn" size entirely and start at 3-6 months.
How to Measure Baby Feet for Shoes
Most pediatricians recommend that babies don't need shoes until they're walking regularly — soft-soled shoes or socks with grips are sufficient for pre-walkers. When your baby does start walking (typically between 9 and 18 months), proper shoe sizing becomes important.
To measure your baby's foot: place their foot flat on a piece of paper, trace around it with a pen held vertically, and measure from the heel to the tip of the longest toe. Add 1 to 1.5 centimeters to this measurement for growing room, then match the total to the foot length column in the shoe size chart.
Baby feet grow rapidly — expect to recheck their size every 2-3 months during the first year of walking. Signs that shoes are too small include red marks on the feet, reluctance to walk, or curled toes.
Sources & References
- World Health Organization (WHO) — Child Growth Standards — International growth charts and weight milestone data used as reference ranges.
- CDC — Clinical Growth Charts — U.S. pediatric growth percentile charts used by American pediatricians.