👶 Child Obesity Index Calculator
Calculate child obesity using the Kaup index and Rohrer index.
Kaup Index (Under 5 years)
Kaup Index = Weight(kg) ÷ Height(m)²
| Index | Grade |
|---|---|
| Under 13 | Malnourished |
| 13 ~ 15 | Thin |
| 15 ~ 18 | Normal |
| 18 ~ 20 | Overweight |
| 20 and over | Obese |
Rohrer Index (Ages 6-18)
Rohrer Index = Weight(kg) ÷ Height(m)³ × 10
| Index | Grade |
|---|---|
| Under 100 | Malnourished |
| 100 ~ 115 | Thin |
| 115 ~ 145 | Normal |
| 145 ~ 160 | Overweight |
| 160 and over | Obese |
Worked examples
A 4-year-old of 100 cm and 16 kg has a Kaup index of 16 ÷ 1.0² = 16.0, which sits in the normal band of 15 to 18.
A 10-year-old of 140 cm and 40 kg has a Rohrer index of 40 ÷ 1.4³ × 10 = 145.8, just inside the overweight band that starts at 145.
What the index assumes
The Kaup index divides weight by height squared and is used for children under five, while the Rohrer index divides by height cubed and is scaled to older children and adolescents. The two scales are not interchangeable, and neither accounts for age- or sex-specific growth curves. A muscular child can read as overweight, so the bands are screening aids, not a diagnosis.
Frequently asked questions
- Why use the cube of height for older children?
- Because body proportions change with growth: weight tracks volume, so dividing by height cubed keeps the index comparable across ages, while height squared suits infants and toddlers.
- What do the cut-off bands mean?
- They sort a single measurement into broad groups. A Kaup index of 13 to 15 suggests thinness and 18 to 20 overweight; for Rohrer 115 to 145 is the usual normal range. Trends over months matter more than one reading.
- Should I worry about a single result?
- No. A recent illness or a growth spurt can shift the number. Paediatric growth charts with BMI-for-age percentiles plus a clinician's assessment remain the reference.