BMI Calculator for Teens (ages 2–19)
Enter DOB or age, sex, height and weight. Instant BMI, percentile, and category.
Reviewed by: Jane Doe, MD, FAAP.
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What this means
Underweight: <5th percentile
Healthy Weight: 5th–85th percentile
Overweight: 85th–95th percentile
Obesity: ≥95th percentile
This is a screening tool, not a medical diagnosis. Consult your healthcare provider.
How does BMI apply to women's health?
BMI (Body Mass Index) is a screening tool that estimates body fat from height and weight. For adolescent girls and young women, BMI must be interpreted differently than for adults because growth, puberty and hormonal changes affect body composition. In teens, BMI is expressed as a percentile that compares a teen’s BMI with peers of the same age and sex — this is called BMI-for-age.
Clinicians use BMI percentiles to spot growth patterns, underweight, or excess weight early; however, BMI does not differentiate muscle from fat and should be considered alongside physical development, activity level, and clinical exam. Always consult a healthcare professional for individualized evaluation.
What is BMI Prime and how is it different from BMI?
BMI Prime is a simple ratio that divides an individual’s BMI by the upper limit of the healthy BMI range (usually 25). It expresses how far someone is above or below the normal BMI boundary: a BMI Prime of 1.0 equals the upper limit of the healthy weight range; values above 1.0 indicate overweight relative to that threshold.
Unlike raw BMI (kg/m²), BMI Prime is unitless and can be helpful to compare relative weight excess between individuals. For teens, however, clinical practice uses percentiles rather than BMI Prime, because teen growth and maturity vary with age and sex.
Are there ethnic considerations for BMI?
Yes. BMI is an imperfect proxy for body fat and may misclassify health risk across different ethnic groups. Research shows that some populations (for example, people of South Asian descent) may have higher body-fat percentages and metabolic risk at lower BMIs than others, while other groups may have higher lean mass.
For teens, clinicians consider ethnicity, family history, and individual growth patterns alongside BMI percentiles. When interpreting BMI, use it as a screening tool and combine it with clinical context, lifestyle factors, and (if needed) more direct measures of body composition.
Explain the BMI formula for pounds and inches
To calculate BMI using pounds and inches, use this formula:
Step-by-step:
- Measure weight in pounds and height in inches.
- Multiply height by itself (height²).
- Divide weight by height².
- Multiply the result by 703 to convert to kg/m² units.
Example: a teen who weighs 120 lb and is 63 in tall has BMI = (120 / (63 × 63)) × 703 ≈ 21.3 kg/m². For teens, convert this BMI to a BMI-for-age percentile (using age and sex) to determine whether that value falls into underweight, healthy weight, overweight, or obesity ranges.