Weight-for-Length Calculator (0–24 Months)
Calculate your baby's weight-for-length percentile and classification using WHO growth standards.
Results
📘 Overview: Weight-for-Length Calculator (0–24 Months)
This Weight-for-Length Calculator assesses whether an infant's weight is appropriate for their length using World Health Organization (WHO) reference data. It’s designed for children aged 0 to 24 months, using gender-specific growth standards.
Unlike BMI, which is used in older children and adults, weight-for-length is the standard for evaluating growth and nutrition in babies. It tells you where your baby falls on the percentile curve, helping you determine if they are underweight, normal weight, overweight, or very overweight for their length.
WHO reference: WHO Child Growth Standards – Weight-for-Length/Height
📐 Formula & Methodology
This tool uses the LMS (Lambda Mu Sigma) method from the WHO growth standards to calculate the Z-score and percentile:
z = [(X / M)^L – 1] / (L × S)
Where:
- X = weight in kg
- M = median weight for a given length
- L = power transformation to normalize data
- S = coefficient of variation
The resulting Z-score is then converted to a percentile using a normal distribution curve (CDF).
📊 Example Calculation
Input: Male infant, 16.5 lbs (7.48 kg), 26.8 in (68.07 cm)
Rounded Length: 68.0 cm
LMS: L = –0.3521, M = 7.7971, S = 0.08256 (from WHO chart)
Z-score: ≈ –0.13
Percentile: ≈ 45.1%
Result: Normal Weight-for-Length
🧠 Use Cases
- 🩺 Pediatric checkups for infants under 2 years old
- 👪 Monitoring baby’s growth at home between doctor visits
- 🏥 Nutritional assessment for infants in clinics or hospitals
- 📈 Public health monitoring for undernutrition or overnutrition
- 📚 Educational demonstrations and research projects
❓ Frequently Asked Questions
📌 What is weight-for-length?
Weight-for-length is a growth measurement used for infants under 2 years old. It compares a baby’s weight to their recumbent length to assess nutritional status.
📌 Why is age not part of the calculation?
Because this metric focuses solely on how a baby’s weight compares to their length, age is not required. WHO provides reference standards based only on length and gender.
📌 What is a healthy weight-for-length percentile?
Percentiles between 5th and 84th are considered normal. Below 5th may indicate underweight, and above 95th may suggest overweight or obesity.
📌 Is the result valid for babies born prematurely?
This calculator uses general WHO reference data. For preterm infants, adjusted growth charts (e.g., Fenton charts) should be used.
📌 What should I do if my baby is under or over the normal range?
Always consult your pediatrician. This tool provides screening information, but your doctor can interpret results in the context of medical history and development.
📌 How often should I check my baby’s growth?
Growth should be monitored regularly, typically during well-baby visits every 1–3 months in the first year and every 3–6 months after that.
📌 Where does the data come from?
This tool uses WHO’s LMS-based z-score tables from the official child growth standard available here: WHO Weight-for-Length Standards.
📌 Does the tool support both metric and imperial units?
Yes. You can enter weight in pounds or kilograms and length in inches or centimeters using the unit selector.