Weight-for-Length/Height Calculator for Babies and Toddlers (WHO)
Through age 5, a child's weight is most usefully compared against their length or height — not their age. This calculator uses the WHO Child Growth Standards for a Z-score, percentile, and interpretation.
⚖️ Weight-for-Length/Height Calculator
WHO Z-score and percentile for babies and young children (0–5 years)
1 Child Information
2 Measurements
What this means
Recommended next step
📖 How to Read Your Result
The Z-score says how far the child's weight sits above or below the median weight for their length or height, measured in standard deviations from the WHO reference. A Z-score of 0 means exactly the median; +1 is one standard deviation above; −1 is one below. About 68% of healthy children fall between −1 and +1, and about 95% between −2 and +2.
| Z-score range | Percentile range | WHO category |
|---|---|---|
| Below −3 | Below 0.1 | Severe wasting |
| −3 to −2 | 0.1 – 2.3 | Wasting |
| −2 to +1 | 2.3 – 84.1 | Normal range |
| +1 to +2 | 84.1 – 97.7 | Possible risk of overweight |
| +2 to +3 | 97.7 – 99.9 | Overweight |
| Above +3 | Above 99.9 | Obese |
📏 Length vs. Height
A child measured lying down reads about 0.7 cm taller than the same child measured standing, because gravity compresses the spine when upright. WHO handles this with two separate charts and switches between them at age 24 months: length on a length board for children under 2, and standing height against a stadiometer for ages 2–5. Right around 24 months either method is valid — use whichever way the child was actually measured, and stay consistent when tracking over time.
⚠️ Limits of the Result
A Z-score is a snapshot, not a diagnosis. It can't tell you the underlying cause of an off-range score (feeding, illness, and genetics all play a role), and it doesn't separate muscle from fat from fluid — a muscular toddler and a child with edema can produce similar numbers for very different reasons. A single reading also rarely tells the whole story; the trend across visits matters far more. And the math assumes accurate inputs — shoes on, slouching, or a poorly zeroed scale can throw the result off by a full category.
💡 Getting a Reliable Reading
Three habits matter most. Measure consistently — same time of day, same method (length or height), same scale across visits. Strip down for weight — babies in just a diaper, toddlers in light clothing only, no shoes (heavy outfits can add half a kilo). Look at the trend, not the snapshot — the shape of the curve across months is what pediatricians read first, not any single number.
🩺 When to Talk to a Pediatrician
Most kids with one off-range Z-score are fine. Worth bringing up at the next visit if the child has crossed two major percentile lines in either direction over a few months, the Z-score sits below −2 or above +2, or wasting (Z below −2) shows up alongside reduced appetite or visible weight loss. None of these is an emergency on its own, but all warrant clinical context.
REFERENCES
Frequently Asked Questions
It compares a young child’s weight with their length or height to see how they measure against children of the same size using WHO growth standards.
No. BMI is typically used for children age 2 and older, while weight-for-length is commonly used for babies and very young children.
Talk to a pediatrician if your child’s result is below −2 or above +2, or if their growth pattern changes quickly over time.
This calculator is designed for babies and young children from birth through age 5.
A Z-score shows how far a child’s weight is above or below the average for their length or height. A score near 0 means close to the median.
