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📘 About the Weight Percentile
Enter your child's sex, date of birth and weight to see where the weight falls on the official growth chart — the same calculation your paediatrician uses. You get the percentile, the z-score (standard deviation score), the median weight for the age and the normal range from the 3rd to the 97th percentile.
Choose the WHO standard (used in India, the UK, Australia and most countries) or the CDC charts (United States). Weight-for-age covers birth to 10 years on WHO charts and birth to 20 years on CDC charts. For premature babies, enter the weeks of pregnancy at birth and the corrected age is used until age 2.
🧮 Formula
✏️ Worked examples
Boy, 6 months, 7.9 kg (WHO)
You get| Weight percentile | 48th percentile |
| What it means | Out of 100 boys of the same age, about 48 have a lower weight and 52 a higher one. |
| Assessment | Within the normal range |
| Z-score (SD score) | -0.06 |
| Median (50th percentile) for this age | 7.95 kg |
| Normal range (3rd–97th percentile) | 6.45 – 9.74 kg |
| Age used | 6 months 1 day |
| Growth chart | WHO (international — used in India, UK, Australia and most countries) |
| Weight entered | 7.9 kg (17.4 lb) |
48th percentile.
Try this example →Girl, 6 months, 6.5 kg (WHO)
You get| Weight percentile | 17th percentile |
| What it means | Out of 100 girls of the same age, about 17 have a lower weight and 83 a higher one. |
| Assessment | Within the normal range |
| Z-score (SD score) | -0.97 |
| Median (50th percentile) for this age | 7.31 kg |
| Normal range (3rd–97th percentile) | 5.82 – 9.22 kg |
| Age used | 6 months 1 day |
| Growth chart | WHO (international — used in India, UK, Australia and most countries) |
| Weight entered | 6.5 kg (14.3 lb) |
17th percentile — Within the normal range.
Try this example →Boy, 4 years, 40 lb (CDC)
You get| Weight percentile | 81st percentile |
| What it means | Out of 100 boys of the same age, about 81 have a lower weight and 19 a higher one. |
| Assessment | Within the normal range |
| Z-score (SD score) | 0.89 |
| Median (50th percentile) for this age | 16.23 kg |
| Normal range (3rd–97th percentile) | 13.23 – 20.87 kg |
| Age used | 4 years 0 months |
| Growth chart | CDC (United States) |
| Weight entered | 18.14 kg (40 lb) |
81st percentile.
Try this example →💡 Which growth chart should I use?
- WHO Child Growth Standards (birth–5 years) show how healthy breastfed children grow in good conditions. They are used in India (recommended by IAP up to 5 years), the UK (UK-WHO charts), Australia, Canada and more than 140 countries.
- From 5 to 19 years this calculator uses the WHO 2007 growth reference. India's IAP 2015 charts and the UK90 charts used after age 4 in the UK are similar but not identical.
- In the United States, the CDC recommends the WHO charts under 2 years and the CDC 2000 charts from 2 to 20 years — choose CDC for those.
💡 Average baby weight by month (WHO median)
- Birth: boys 3.3 kg, girls 3.2 kg
- 3 months: boys 6.4 kg, girls 5.8 kg
- 6 months: boys 7.9 kg, girls 7.3 kg
- 9 months: boys 8.9 kg, girls 8.2 kg
- 12 months: boys 9.6 kg, girls 8.9 kg
- 2 years: boys 12.2 kg, girls 11.5 kg
❓ Frequently asked questions
What does percentile mean on a growth chart?
It compares your child with 100 children of the same age and sex. The 60th percentile means your child measures more than 60 of them and less than 40.
Is the 50th percentile the goal?
No. Any percentile between about the 3rd and 97th can be healthy. What matters is that your child grows steadily along roughly the same curve.
Should I use corrected age for a premature baby?
Yes. Enter the weeks of pregnancy at birth and the calculator uses corrected age until 2 years, as doctors do.
What is a normal weight for a 6-month-old?
On the WHO chart the median is about 7.9 kg for boys and 7.3 kg for girls; the normal range is roughly 6.4–9.7 kg for boys and 5.8–9.2 kg for girls.
My baby dropped percentiles — should I worry?
Small shifts are common, especially in the first months. Crossing two major lines (for example from the 50th to below the 9th) is worth checking with your doctor.