Learn to calculate your Body Mass Index (BMI) using height and weight, and understand what the number means for your health.
Step-by-Step Guide
Understand the BMI Formula
BMI = weight (kg) ÷ height (m)². For example, a person who weighs 70 kg and stands 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. Simple arithmetic — no special tools required.
Measure Your Height Accurately
Remove shoes and stand flat against a wall. Rest a book horizontally on top of your head and mark the wall. Measure from the floor to the mark in centimetres, then divide by 100 to convert to metres.
Record Your Weight
Weigh yourself first thing in the morning before eating, wearing minimal clothing. Use a digital scale on a hard, flat surface. Note the value in kilograms (divide pounds by 2.205 to convert).
Calculate and Round
Square your height in metres: e.g. 1.75² = 3.0625. Divide your weight by that result: 70 ÷ 3.0625 = 22.9. Round to one decimal place.
Interpret Your Result
WHO thresholds for adults: below 18.5 = Underweight | 18.5–24.9 = Normal weight | 25–29.9 = Overweight | 30 or above = Obese. BMI is a screening tool — it does not account for muscle mass, age, or ethnicity.
Try Our Free Tool
BMI Calculator
Frequently Asked Questions
Q: Can I use pounds and inches?
A: Yes. The imperial formula is BMI = (weight in lbs × 703) ÷ (height in inches)². Our BMI Calculator supports both metric and imperial.
Q: Is BMI accurate for athletes?
A: Not always. Muscle weighs more than fat, so muscular people may have a high BMI without excess body fat. Consider body-fat percentage or waist-to-hip ratio for a fuller picture.
Q: Does BMI apply to children?
A: No. Children and teenagers (ages 2–19) use age- and sex-specific percentile charts rather than the standard adult thresholds.