WHO Child Growth Standards are international benchmarks developed by the World Health Organization using data from healthy, breastfed children across six countries. They describe how children should grow under optimal conditions, rather than simply averaging population data. These standards are used globally to monitor growth in children aged 0–5 years.

A percentile indicates where a child's measurement falls compared to other children of the same age and sex. For example, if a child is at the 75th percentile for weight, they weigh more than 75% of children and less than 25% of children in the reference population. The 50th percentile is the median. Percentiles between the 3rd and 97th are generally considered within the normal range.

You should consult a pediatrician if: (1) Your child's weight or height crosses two major percentile lines (e.g., dropping from the 75th to the 25th percentile), (2) Measurements fall below the 3rd percentile or above the 97th percentile, (3) Your child's growth pattern suddenly flattens or accelerates dramatically, or (4) Weight-for-height/BMI indicates possible undernutrition or obesity. A single measurement outside the normal range doesn't necessarily indicate a problem—trends over time matter most.

Length is measured with the child lying down (recumbent position) and is used for children under 2 years of age. Height is measured with the child standing upright and is used for children 2 years and older. Length measurements are typically about 0.5–1 cm longer than standing height for the same child. WHO provides separate standards for length (0–24 months) and height (24–60 months).

This tool uses approximate WHO percentile data and provides a reliable estimate for screening purposes. It is suitable for tracking growth trends at home. However, it should not replace professional medical assessment. Pediatricians use official WHO charts with precise data points and can interpret results in the context of your child's complete health history, genetics, and development.

BMI-for-age is used to screen for overweight and underweight in children aged 2–5 years. Unlike adult BMI (which uses fixed cutoffs), children's BMI is interpreted using age- and sex-specific percentiles. A BMI-for-age above the 85th percentile may indicate overweight, above the 95th may indicate obesity, and below the 5th percentile may indicate underweight. BMI is calculated as weight(kg) / height(m)².