Home › Health, Fitness & Education › Baby Percentile Calculator
Baby Percentile Calculator
Use this free baby percentile calculator to see how your baby's growth compares with the WHO Child Growth Standards. Enter your baby's age in months, sex, weight, length, and head circumference, and the calculator shows the percentile for each measurement — plus a simple chart showing where your baby falls.
Weigh your baby without clothes on a baby scale. Measure length lying flat, head to heel, and head circumference around the widest part of the head.
| Weight-for-age | 50th percentile |
| Length-for-age | 50th percentile |
| Head circumference-for-age | 50th percentile |
| Median weight at this age | 9.6 kg |
How it works
A percentile compares your baby with other babies of the same age and sex. If your baby is on the 50th percentile for weight, half of babies the same age weigh less and half weigh more. If your baby is on the 25th percentile, 25 out of 100 babies weigh less. The reference for this comparison is the WHO Child Growth Standards, published by the World Health Organization and based on healthy, breastfed children from six countries. The standards give the 3rd, 50th, and 97th percentile values for weight-for-age, length-for-age, and head-circumference-for-age for boys and girls from birth to 24 months.
This calculator holds those reference values at the ages 0, 1, 2, 3, 6, 9, 12, 15, 18, 21, and 24 months, separately for boys and girls. For an age between two reference months — say 4 months — it interpolates, which means it draws a straight line between the values at 3 and 6 months and reads off the value at 4 months. Then it compares your baby's measurement with the 3rd, 50th, and 97th values at that age: a value equal to the 50th value is the 50th percentile, a value halfway between the 3rd and the 50th is about the 26th percentile, and a value halfway between the 50th and the 97th is about the 73rd percentile. Values below the 3rd or above the 97th are shown as below the 3rd or above the 97th percentile.
Weight in pounds is converted to kilograms (divide by 2.20462) and length in inches to centimeters (multiply by 2.54) before the comparison, because the WHO standards are in metric units. Head circumference is entered in centimeters only, since that is how it is always measured. The chart beside the calculator shows the three percentiles as dots on a scale from the 3rd at the bottom to the 97th at the top, with a dashed line at the 50th — so you can see at a glance whether weight, length, and head size sit together or whether one is much higher or lower than the others.
Percentiles are not grades, and there is no single right one. Healthy babies grow along many different lines: a baby who has always been on the 10th percentile and stays there is usually growing just fine, while a baby who was on the 75th and falls to the 25th over a few months deserves a closer look. What matters most is the pattern over time, steady growth, and how the baby is doing overall — feeding well, alert, and meeting milestones. One measurement on one day, especially one taken at home, is only a rough guide.
Worked example
A 12-month-old boy weighs 9.6 kg, is 75.7 cm long, and has a head circumference of 46.1 cm.
Step 1: Look up the WHO values for a 12-month-old boy. The median (50th percentile) weight is 9.6 kg, the median length is 75.7 cm, and the median head circumference is 46.1 cm.
Step 2: Compare weight. His weight of 9.6 kg exactly matches the median of 9.6 kg, so his weight-for-age percentile is the 50th.
Step 3: Compare length. His length of 75.7 cm exactly matches the median of 75.7 cm, so his length-for-age percentile is the 50th.
Step 4: Compare head circumference. His head of 46.1 cm exactly matches the median of 46.1 cm, so his head-circumference-for-age percentile is the 50th.
The tool shows the same result: all three measurements on the 50th percentile, right in the middle of the WHO range for a 12-month-old boy. If he had weighed 8.2 kg instead, his weight would sit between the 3rd percentile (7.78 kg) and the median (9.6 kg), at about the 14th percentile.
FAQ
What is a baby percentile?
A baby percentile compares your baby with other babies of the same age and sex, using the WHO Child Growth Standards. If your baby is on the 50th percentile for weight, half of babies the same age weigh less and half weigh more. If your baby is on the 25th percentile, 25 out of 100 babies weigh less and 75 weigh more. Percentiles describe where a baby sits in the range, not a grade — healthy babies grow along many different percentile lines.
What are the WHO Child Growth Standards?
The WHO Child Growth Standards are reference charts published by the World Health Organization, based on healthy, breastfed children from six countries. They show how children grow when their health, food, and care are good. This calculator uses those standards for weight-for-age, length-for-age, and head-circumference-for-age for boys and girls from birth to 24 months, with values interpolated between the reference months.
What percentile should my baby be on?
There is no single right percentile. Healthy babies can sit anywhere from about the 3rd to the 97th percentile, and what matters most is that your baby keeps growing steadily along roughly the same percentile line over time. A baby who has always been on the 10th percentile and stays there is usually growing fine, while a baby who drops across two percentile lines deserves a check with a doctor.
How do I measure my baby's length and head circumference?
Weigh your baby on a baby scale, without clothes, for the most accurate weight. For length, lay your baby flat on a firm surface, hold the head gently against a fixed end, straighten the legs, and measure to the heels. For head circumference, wrap a soft tape around the widest part of the head — just above the eyebrows and ears, around the back of the head — and read the number where the tape meets itself.
My baby is below the 3rd or above the 97th percentile — should I worry?
Not on one measurement alone. Percentiles outside the 3rd to 97th range are uncommon but not automatically a problem, especially if your baby is feeding well, alert, and growing steadily. What matters is the pattern over time and how your baby is doing overall. Take the results to your pediatrician, who can measure your baby properly and look at the full growth record.