⚖️ Average Weight at 3 Months
According to Medical News Today, at 3 months the 50th percentile (i.e., the average) is:
- Girls: ~12 lb 14 oz (≈ 5.8 kg)
- Boys: ~14 lb 1 oz (≈ 6.4 kg) unitypoint.orgparents.com+2medicalnewstoday.com+2cdc.gov+2
This means half of U.S. babies weigh less, and half weigh more.
📊 Weight Percentiles & What They Mean
Percentiles compare your baby’s weight to others the same sex and age:
- < 5th percentile: smaller than 95% of peers
- 50th percentile: right in the middle
- > 95th percentile: larger than 95%
For example, a 3‑month‑old at the 40th percentile weighs more than 40% of peers but less than 60% infantchart.com+2babycentre.co.uk+2guavahealth.com+2cdn.who.int.
You can track percentiles using U.S. CDC or WHO growth charts. The WHO charts are standard for infants under 2 years in the U.S. parents.com+2parents.com+2guavahealth.com+2.
📈 Expected Weight Gain Pattern
From birth to 3 months, typical growth patterns include:
- Gaining about 1 oz per day, roughly 4.5–6 lb by 3 months cdc.gov+15parents.com+15babycentre.co.uk+15.
- Usually double birth weight by 4–6 months medicalnewstoday.com+3parents.com+3unitypoint.org+3.
🧩 U.S. Growth Chart Tools & Monitoring
For precise percentile tracking:
- Use CDC weight-for-age charts (boys & girls, 0–36 mo) infantchart.cominfantchart.com+7cdc.gov+7brightfutures.org+7
- Try online calculators (e.g., PediTools, Baby Centre) by inputting sex, age, and weight unitypoint.org+8peditools.org+8cdc.gov+8
Regular well-baby checkups will plot weight growth over time. Consistency and trend matter more than single data points parents.com.
✅ What’s Considered Healthy?
- A healthy 3‑month‑old typically weighs between:
- Girls: ~9 lb 6 oz to 15 lb (≈ 4.2–6.8 kg)
- Boys: ~10 lb to 16 lb (≈ 4.5–7.3 kg) cdc.gov+15medicalnewstoday.com+15babycentre.co.uk+15
- As long as your baby is following their percentile curve and meeting feeding/development milestones, that’s a strong sign of healthy growth.
💡 Tips for Parents
- Track over time – steady growth along a curve is key.
- Feeding matters – formula-fed babies may gain faster than breastfed ones after the first two months parents.com+1parents.com+1.
- Know what percentiles mean – being in the 10th or 90th percentile isn’t inherently problematic babycentre.co.uk+1guavahealth.com+1.
- Consult your pediatrician if your baby crosses more than two percentile lines, shows inconsistent growth, or seems lethargic—sometimes this signals underlying issues.
📝 Summary Table
| Metric | Girls (avg) | Boys (avg) |
|---|---|---|
| 3‑month average weight | ~12 lb 14 oz (5.8 kg) | ~14 lb 1 oz (6.4 kg) |
| Typical weight range | ~9.5 – 15 lb | ~10 – 16 lb |
| Expected gain since birth | ~4.5–6 lb | similar |