Note: This tool checks your baby’s height and weight percentiles together, so use the Baby Weight Percentile Calculator instead when you only want to check weight, or the Baby Height and Head Circumference Percentile Calculator when you want to check height and head size.
Baby Height and Weight Percentile Calculator
See how your baby's weight and length compare with healthy babies of the same age and sex, using the WHO Child Growth Standards.
Born early? (optional, corrected age)
For babies born before 37 weeks, growth is usually plotted by corrected age until 24 months.
A percentile is not a grade. The 50th percentile is the middle, and healthy babies can be anywhere from the 2nd to the 98th. Doctors look at the pattern over several visits, and at birth history and parents' heights. Based on the WHO Child Growth Standards. Please talk to your doctor if you are worried.
How to use
- Choose kg and cm, or lb and inches, and select boy or girl.
- Enter your baby's date of birth (or age in months) and the date of measurement.
- Enter weight, length or both. One is enough.
- Press Calculate to see percentiles, status and a growth chart.
- Tap the chart buttons to switch between weight, length and weight-for-length.
Baby Height and Weight Percentile Calculator
What Is Normal Growth?
“Your baby is in the 30th percentile.” Many parents hear this at a check-up and feel unsure. Is that good? Is it low? Our free baby height and weight percentile calculator shows where your baby stands, and this guide explains what the numbers really mean.
What Does a Percentile Mean?
A percentile compares your baby with other babies of the same age and sex. If your baby is on the 30th percentile for weight, 30 out of 100 babies weigh less and 70 weigh more. The 50th percentile is the middle.
A percentile is not a grade. A baby on the 15th percentile is not “worse” than a baby on the 85th. What matters most is that your baby follows their own curve over time.
Which Growth Chart Does the Calculator Use?
We use the WHO Child Growth Standards. They describe how healthy children should grow when they are well fed and cared for. The data comes from breastfed babies in six countries: Brazil, Ghana, India, Norway, Oman and the USA.
The CDC advises US doctors to use the WHO charts for all babies up to 2 years, whatever they are fed. After age 2, US doctors switch to the CDC charts. Our calculator keeps using WHO standards up to 5 years, as many countries do.
Average Weight and Length by Age
These values come from the WHO tables. The brackets show the 3rd to 97th percentile, which is the range where almost all healthy babies fall.
Boys
| Age | Weight (median) | Length (median) |
|---|---|---|
| Birth | 3.3 kg (2.5 to 4.3) | 49.9 cm (46.3 to 53.4) |
| 3 months | 6.4 kg (5.1 to 7.9) | 61.4 cm (57.6 to 65.3) |
| 6 months | 7.9 kg (6.4 to 9.7) | 67.6 cm (63.6 to 71.6) |
| 9 months | 8.9 kg (7.2 to 10.9) | 72.0 cm (67.7 to 76.2) |
| 12 months | 9.6 kg (7.8 to 11.8) | 75.7 cm (71.3 to 80.2) |
| 18 months | 10.9 kg (8.9 to 13.5) | 82.3 cm (77.2 to 87.3) |
| 24 months | 12.2 kg (9.8 to 15.1) | 87.8 cm (82.1 to 93.6) |
Girls
| Age | Weight (median) | Length (median) |
|---|---|---|
| Birth | 3.2 kg (2.4 to 4.2) | 49.1 cm (45.6 to 52.7) |
| 3 months | 5.8 kg (4.6 to 7.4) | 59.8 cm (55.8 to 63.8) |
| 6 months | 7.3 kg (5.8 to 9.2) | 65.7 cm (61.5 to 70.0) |
| 9 months | 8.2 kg (6.6 to 10.4) | 70.1 cm (65.6 to 74.7) |
| 12 months | 8.9 kg (7.1 to 11.3) | 74.0 cm (69.2 to 78.9) |
| 18 months | 10.2 kg (8.2 to 13.0) | 80.7 cm (75.2 to 86.2) |
| 24 months | 11.5 kg (9.2 to 14.6) | 86.4 cm (80.3 to 92.5) |
Notice how wide the healthy range is. At 12 months, a boy can weigh anywhere from 7.8 to 11.8 kg and still be growing normally.
What Is Weight for Length?
Weight alone does not tell the full story. A tall baby naturally weighs more than a short one. For this reason, doctors also check weight for length, which compares your baby’s weight with their body length.
For children under 2, the WHO and CDC treat a weight-for-length below the 2nd percentile as low, and above the 98th as high. Our calculator shows this for you when you enter both measurements.
How the Calculator Works
The calculator uses the LMS method that WHO and CDC both rely on. Each age has three numbers: L, M and S. They describe the typical value and how it spreads. Your baby’s z-score is ((measurement ÷ M)^L − 1) ÷ (L × S), and the z-score becomes a percentile.
We use the WHO weekly tables for babies under 13 weeks, because growth is fast at this age. After that, we use the monthly tables.
How to Measure Your Baby Correctly
Accurate numbers give accurate percentiles. Follow these points from the American Academy of Pediatrics:
- Under 2 years: measure length lying down, ideally with two people.
- If your baby is measured standing: add 0.7 cm to get the length. Standing height is about 0.7 cm less than lying length.
- From 2 years: measure standing height. If the child is measured lying down, subtract 0.7 cm.
- Weight: use a clean, calibrated scale and the same one each time.
You can also tick the correct option in the calculator, and it adjusts for you.
Premature Babies and Corrected Age
If your baby was born before 37 weeks, growth is usually plotted by corrected age until about 24 months. Corrected age means actual age minus the weeks born early. Check your baby’s real and corrected age with the Baby Age Calculator.
What Matters More Than One Number?
One measurement is a snapshot. The growth pattern across several visits tells the real story. Doctors usually take a closer look when a baby moves across two or more main percentile lines, up or down.
Parents’ heights and birth history also matter. A baby with tall parents is likely to track higher. See what to expect with the Baby Adult Height Predictor.
Switching from length to height at 24 months can also make a child seem to drop a percentile. This is usually a measuring change, not a growth problem.
When to Talk to Your Doctor
Please speak to your doctor if:
- Your baby is below the 2nd or above the 98th percentile
- Your baby crosses two major percentile lines over a few months
- Weight gain has stopped or your baby is losing weight
- Your baby feeds poorly, vomits often or seems unwell
Feeding, Pregnancy and Growth
Feeding shapes weight gain in the first year. A routine helps, and the Baby Feeding Reminder can keep feeds on track. Growth also starts before birth. Healthy weight gain in pregnancy supports your baby’s birth weight, which you can check with the Pregnancy Weight Gain Calculator, the Pregnancy Calorie and Protein Calculator and the BMI Calculator.
During pregnancy, track growth with Baby Size by Week, the Pregnancy Week by Week Calculator and the Gestational Age Calculator. Your due date comes from the Due Date Calculator, and your scan may change it, as the Ultrasound Due Date Calculator shows.
Planning a baby or just starting out? Try the Ovulation Calculator, Safe Period Calculator, Pregnancy Test Date Calculator, Conception Due Date Calculator or IVF Due Date Calculator. Later, the Kick Counter, Contraction Timer, Hospital Bag Checklist, Baby Budget Calculator and Baby Name Generator will help.
To check head size as well, use our Baby Height and Head Circumference Percentile Calculator.
Frequently Asked Questions
What is a good percentile for a baby?
Any percentile from the 2nd to the 98th can be healthy. Steady growth along one curve matters most.
Is the 50th percentile best?
No. It is simply the middle. Many healthy babies are above or below it.
Why did my baby’s percentile drop?
Small changes are common, especially in the first months and when switching from length to height at 24 months. Large drops across two main lines need a doctor’s review.
Do breastfed and formula-fed babies use the same chart?
Yes. The CDC recommends the WHO charts for all babies up to 2 years, whatever they are fed.
Does the calculator work for preemies?
Yes. Enter the birth week to use corrected age.
Sources: WHO Child Growth Standards; CDC, Use and Interpretation of the WHO and CDC Growth Charts; American Academy of Pediatrics guidance on anthropometric measurements.