Child Growth LabBaby Percentile Calculator
WHO Child Growth Standards · Birth to under 2 years
Compare an infant's weight, recumbent length, weight-for-length, and optional head circumference with sex-specific WHO growth standards using exact age in days.
Pediatric growth calculators based on CDC and WHO growth standards.
Who it is for
Parents and clinicians
For parents tracking infant growth and clinicians who need a quick reference comparison from published standards.
Measurements needed
Weight and recumbent length
Enter a dated weight and length measured while lying down. Head circumference is optional and adds a fourth reference result.
WHO vs CDC
The reference changes at age 2
This tool uses WHO standards before the second birthday. From age 2, use the CDC Growth Chart Calculator.
Understanding the results
Each percentile compares one measurement with the WHO reference for children of the same sex and exact age, or with the weight-for-length reference at the same recumbent length. Results should be considered alongside measurement quality and change over time.
The percentile expresses position on the reference distribution. The z-score expresses the same position in standard-deviation units, with zero at the reference median. Neither value describes a growth trend from a single measurement.
This calculator is based on WHO Child Growth Standards and is not affiliated with or endorsed by WHO.
How it works
Date of birth and measurement date are converted to an exact integer age in days. The calculator selects the published sex-specific WHO L, M, and S parameters, applies the WHO LMS calculation, and converts the resulting z-score to a percentile.
Weight-for-length uses the two adjacent 0.1 cm WHO keys when a length falls between table rows. Weight-based results apply the WHO igrowup extension outside ±3 z before percentile conversion.
Applicable age range
From birth through the day before the second birthday. On and after the second birthday, use the CDC growth calculators for children aged 2 years and older. WHO and CDC results are not automatically mixed.
Worked example
In the WHO-published igrowup sample, a 50-day-old girl measuring 5.3 kg, 57.1 cm in recumbent length, and 37.6 cm in head circumference produces z-scores of 0.72 for weight-for-age, 0.57 for length-for-age, 0.40 for weight-for-length, and −0.09 for head circumference-for-age.
Limitations
- Results depend on accurate dates and carefully taken measurements.
- Use recumbent length, not standing height, for this calculator.
- A single percentile does not describe a growth trend.
- Corrected age for prematurity is not applied automatically.
- This reference tool does not replace care from a licensed clinician.
References and attribution
- World Health Organization — WHO Child Growth Standards
- World Health Organization — Child growth standards software and LMS resources
- WHO Child Growth Standards data used under Permission Request 202609680, granted 2026-07-16.
No WHO logo is used. Child Growth Lab is independent and is not affiliated with or endorsed by WHO.
FAQ
- What does the baby percentile calculator measure?
- It calculates weight-for-age, length-for-age, and weight-for-length percentiles. Head circumference-for-age is also calculated when a head measurement is entered.
- Which growth standards are used?
- The calculations use the WHO Child Growth Standards for boys and girls from birth until the second birthday.
- Why does the calculator ask for recumbent length?
- The WHO birth-to-2 length standards use length measured while the child is lying down. Standing height is a different measurement method.
- What happens on the second birthday?
- WHO results stop before the second birthday on this site. Use the CDC growth calculators from the second birthday onward.
- Does a percentile provide medical advice?
- No. A percentile is a reference comparison from published growth standards and does not replace evaluation by a licensed clinician.
Content maintenance date: 2026-07-16. Editorial and methodology review: see Editorial and methodology review.