Infant Growth Percentile Calculator
Weight, length and head circumference percentiles for babies 0-24 months.
Enter your values
Choose one of: Boy, Girl.
Enter the age in months.
Enter the weight in kg.
Enter the length in cm.
Enter the head circumference in cm.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Weight percentile
- 53.3th (z = 0.08)
- Length percentile
- 83.1th (z = 0.96, median 64.8 cm)
- Head circumference percentile
- 52.8th (z = 0.07, median 43.4 cm)
- Median weight at this age
- 7.83 kg
- Median length at this age
- 64.8 cm
- Healthy range (3rd-97th)
- 6.21 - 9.45 kg
Working
- 1z = (7.9 - 7.83) / 0.86 = 0.08
Quick answer
Growth percentiles compare a baby with WHO reference data for the same age and sex. A z-score of 0 is the median, and anything between the 3rd and 97th percentile is usually normal.
z = (measure - median) / SD; percentile = normal CDF(z)
At a glance
| What it does | Weight, length and head circumference percentiles for babies 0-24 months. |
|---|---|
| Category | Health |
| Inputs needed | Sex, Age, Weight, Length, Head circumference |
| Main output | Weight percentile |
| Formula | z = (measure - median) / SD; percentile = normal CDF(z) |
| Cost | Free — no sign-up, no download |
How to use the Infant Growth Percentile Calculator
- 1Enter your baby's age in months, using decimals for part months such as 6.5.
- 2Add weight in kilograms and length and head circumference in centimetres.
- 3Look at the trend across visits rather than a single percentile reading.
Inputs explained
- Sex
- Choose one of: Boy, Girl.
- Age(months)
- Enter the age in months.
- Weight(kg)
- Enter the weight in kg.
- Length(cm)
- Enter the length in cm.
- Head circumference(cm)
- Enter the head circumference in cm.
Worked example
Using the values the calculator loads with:
Inputs
- SexBoy
- Age6 months
- Weight7.9 kg
- Length67 cm
- Head circumference43.5 cm
Results
- Weight percentile53.3th (z = 0.08)
- Length percentile83.1th (z = 0.96, median 64.8 cm)
- Head circumference percentile52.8th (z = 0.07, median 43.4 cm)
- Median weight at this age7.83 kg
- Median length at this age64.8 cm
- Healthy range (3rd-97th)6.21 - 9.45 kg
- z = (7.9 - 7.83) / 0.86 = 0.08
Frequently asked questions
Is a low percentile a problem?
Not on its own. A baby steadily tracking the 10th percentile is usually fine; a baby crossing down through two percentile bands is what prompts a review.
Are these exact WHO tables?
They are close smooth approximations of the WHO 0-24 month standards for quick checks. Your clinic's printed chart remains the reference for medical decisions.
What do I need to enter into the Infant Growth Percentile Calculator?
Just 5 values: sex, age, weight, length, head circumference. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Infant Growth Percentile Calculator work out the answer?
Growth percentiles compare a baby with WHO reference data for the same age and sex. A z-score of 0 is the median, and anything between the 3rd and 97th percentile is usually normal. It applies the formula z = (measure - median) / SD; percentile = normal CDF(z) and shows the working so you can check each step by hand.
Is the Infant Growth Percentile Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.