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Health
Grade 7-12
Body Mass Index & Body Composition Cheat Sheet
A printable reference covering BMI formula, BMI categories, body composition, waist measurements, and healthy interpretation for grades 7-12.
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Body Mass Index, or BMI, is a screening tool that compares a person’s mass to their height. This cheat sheet helps students calculate BMI, understand what the number can and cannot tell them, and connect it to overall health. It also explains body composition, which gives a more complete picture than weight alone. Students need this reference to use health measurements responsibly and avoid judging health from appearance or one number.
Key Facts
- BMI using metric units is BMI = weight in kilograms / (height in meters x height in meters).
- BMI using U.S. units is BMI = 703 x weight in pounds / (height in inches x height in inches).
- For adults, BMI below 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25.0 to 29.9 is overweight, and 30.0 or higher is obesity.
- For children and teens, BMI is interpreted using age and sex percentiles rather than adult category cutoffs.
- Body composition describes what the body is made of, including fat mass, muscle, bone, water, and organs.
- A person with more muscle may have a higher BMI without having excess body fat, because muscle is dense.
- Waist circumference can help estimate health risk related to abdominal fat, but it should be interpreted with other health information.
- Healthy body assessment should include habits, growth, fitness, nutrition, sleep, medical history, and professional guidance, not BMI alone.
Vocabulary
- Body Mass Index
- Body Mass Index, or BMI, is a number calculated from height and weight that is used to screen for possible weight-related health risks.
- Body Composition
- Body composition is the proportion of fat, muscle, bone, water, and other tissues in the body.
- Fat Mass
- Fat mass is the total amount of body tissue made up of stored fat.
- Lean Mass
- Lean mass is body weight that is not fat, including muscle, bone, organs, and body water.
- Percentile
- A percentile shows how a measurement compares with a reference group, such as students of the same age and sex.
- Waist Circumference
- Waist circumference is the distance around the waist and can help estimate the amount of abdominal fat.
Common Mistakes to Avoid
- Using adult BMI categories for teens is wrong because teen BMI must be compared with age and sex percentiles.
- Forgetting to square height in the BMI formula is wrong because BMI depends on height x height, not height alone.
- Mixing pounds with the metric formula is wrong because BMI = weight in kilograms / height in meters squared requires metric units only.
- Treating BMI as a diagnosis is wrong because BMI is only a screening tool and cannot directly measure body fat, fitness, or health.
- Assuming all weight gain is unhealthy is wrong because growth, puberty, muscle gain, hydration, and normal development can all change weight.
Practice Questions
- 1 Calculate the BMI of a person who weighs 60 kg and is 1.65 m tall using BMI = weight in kilograms / (height in meters x height in meters).
- 2 Calculate the BMI of a person who weighs 150 lb and is 65 in tall using BMI = 703 x weight in pounds / (height in inches x height in inches).
- 3 An adult has a BMI of 27.2. Which adult BMI category does this fall into, and why?
- 4 Two students have the same BMI, but one has more muscle and the other has less physical activity. Explain why BMI alone cannot tell which student is healthier.