HowToCalculateBMI.org

Teaching BMI

Written by the HowToCalculateBMI.org team Updated 1 min read

Checked against 1 cited source

This free 45-minute lesson plan teaches students how to calculate BMI in metric and imperial units, what it means, and what it can't tell you. It uses made-up people, not students' own measurements, and ends with a discussion of BMI's limits. It fits a middle or high school math class (formulas, squaring, unit conversion, division) or a health class.

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Learning objectives

By the end of the lesson, students can:

  1. Calculate BMI from height and weight in metric and imperial units.
  2. Explain why height is squared and what the 703 factor does.
  3. Name the adult BMI categories and explain why children use percentiles.
  4. Describe at least two things BMI can't measure.

45-minute outline

Time Activity
0–5 min Hook: "Two people both weigh 200 lb. Are they the same size?" Discuss why height matters.
5–15 min Teach the formula: BMI = kg ÷ m², then the imperial version with 703. Work one example of each on the board. Worked examples.
15–30 min Practice: students complete a printed worksheet in pairs, or use practice mode on devices.
30–40 min Discussion: what BMI misses. Use the muscle vs. BMI tool to show two people with the same BMI and very different bodies.
40–45 min Exit ticket: one calculation and one sentence on a limitation of BMI.

Teaching weight topics sensitively

  • Use fictional data. Don't ask students to weigh or measure themselves in class or share their numbers.
  • Children use percentiles, not adult categories. Make clear that adult categories don't apply to them.1 BMI for kids.
  • Talk about health, not appearance. Frame BMI as a screening tool scientists and doctors use, not a judgment of anyone's body.
  • Know where to point students. Some students may be dealing with eating concerns; know your school's counselor or nurse contacts.

Discussion questions

  1. Why do you think the formula divides by height squared rather than just height? The formula.
  2. A rugby player has a BMI of 30. Does that mean he's unhealthy? Why or why not?
  3. Why might doctors use different BMI cutoffs for different groups? Asian BMI.
  4. BMI was invented in the 1830s for statistics, not medicine. Does that matter? History of BMI.

Extensions

  • Spreadsheets: build a BMI calculator in Excel or Google Sheets. BMI in Excel.
  • Programming: write a BMI function in Python or JavaScript. BMI in code.
  • Statistics: explore how percentiles and z-scores work. BMI percentiles.

Sources

  1. CDC ↩

Further reading

Written by

The HowToCalculateBMI.org team

We explain BMI in plain language, check every worked example with automated tests, and keep each page up to date with current guidelines.

How we write and check our pages

Kept up to dateLast updated October 9, 2026

This page is for education and is not medical advice. Talk with a healthcare professional about your weight and health.

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