Health July 13, 2026 · 8 Min Read

Baby Weight Calculator – Guide & Formulas

Monitor and track your infant's growth weight percentile using WHO and CDC growth standards for boys and girls.

Tracking an infant's weight is an essential way to monitor their nutrition, development, and overall physical health during the critical first years. This Baby Weight Calculator matches your baby's weight and age against the official World Health Organization (WHO) growth standards (for infants aged 0 to 24 months) or CDC charts.

Key Takeaway

Use the free Baby Weight Calculator to monitor and track your infant's growth weight percentile using who and cdc growth standards for boys and girls. Get instant results with step-by-step explanations.

How to Use the Baby Weight Calculator

  1. Select your baby's biological sex (Boy or Girl).
  2. Enter your baby's age in weeks or months.
  3. Input the current weight in pounds, ounces, or kilograms.
  4. Review your baby's growth percentile and developmental trajectory description.

The Formula

Percentile is computed using the standard LMS method from clinical WHO database parameters mapping age and sex.

Variable Definitions

  • L: L-parameter representing skewness in WHO growth references
  • M: M-parameter representing median weight at the given age
  • S: S-parameter representing coefficient of variation

Determining Infant Growth Percentile

A 6-month-old baby girl weighs 16.1 lbs (7.3 kg).

  1. Step 1: Set Age = 6 months, Sex = Female, Weight = 7.3 kg.
  2. Step 2: Reference the WHO 6-month female weight parameters: L=-0.14, M=7.3, S=0.11.
  3. Step 3: Plug into the LMS equation: Z-score is approximately 0.
  4. Step 4: A Z-score of 0 corresponds exactly to the 50th percentile.
  5. Step 5: This indicates the baby's weight is perfectly average for her cohort.

Frequently Asked Questions

Is it bad if my baby is in a low percentile?

Not necessarily. Every baby grows at their own individual pace. What matters most is that your baby continues to grow along their own established curve, rather than dropping significantly across percentiles over time.

How often should I weigh my baby?

For healthy babies, weighing during routine pediatrician check-ups (typically at birth, 1 month, 2, 4, 6, 9, 12, 18, and 24 months) is usually sufficient. Avoid daily weighing at home as normal daily fluid cycles can create unnecessary anxiety.