Weight-for-Age Calculator
Child weight percentile and z-score from 0 to 19 years. Free, private and instant.
How to use the Weight-for-Age
- Pick metric (cm, kg) or imperial (ft, in, lb) units.
- Choose child is a: Boy or Girl.
- Enter age in years and months.
- Enter weight.
- Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.
About the Weight-for-Age
Weight-for-age compares a child's weight with other children of the same age and sex. Enter age, sex and weight to see the percentile, z-score and where the child sits on the growth curves.
Also known as: weight for age percentile, child weight percentile calculator, WHO weight-for-age chart.
Worked example
- Child is a: Boy
- Age: 5 years
- Weight: 18.5 kg
Weight-for-age percentile: 53rd percentile (Healthy weight). At 5 years, 18.5 kg is heavier than about 53% of boys the same age (z-score 0.08).
- Percentile: 53rd
- Z-score: 0.08
- Median weight: 18.3 kg
- Typical range (3rd-97th): 14.2 - 23.6 kg
Formula and cut-offs
Percentile is derived from a z-score: z = ln(weight / median) / sigma, using approximate WHO reference medians for each age and sex, then converted to a percentile. Results are estimates.
Frequently asked questions
What is a normal weight percentile for a child?
Anything between the 3rd and 97th percentile is generally normal. What matters most is that a child follows their own growth curve over time.
Does a low percentile mean something is wrong?
Not by itself. Healthy children can be on low or high percentiles. See a paediatrician if the child crosses percentile lines or you are concerned.
What is the difference between percentile and z-score?
A z-score shows how many standard deviations a measurement is from the median for age and sex. A percentile is the same thing on a 0 to 100 scale: the 50th percentile is a z-score of 0, and the 3rd percentile is about -1.88.
What is the weight-for-age percentile for a 5-year-old boy and 18.5 kg?
Weight-for-age percentile: 53rd percentile (Healthy weight). At 5 years, 18.5 kg is heavier than about 53% of boys the same age (z-score 0.08). Enter your own numbers above for a personal result.
Sources and references
Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.
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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.