How to Calculate BMI (Formula + What It Means)
Updated June 2026
Calculate body mass index.
BMI (body mass index) is a quick screening number based on your height and weight. Here's the formula and how to read the result.
The formula
Metric:
BMI = weight (kg) ÷ height (m)²
Imperial:
BMI = 703 × weight (lb) ÷ height (in)²
Worked example
Someone 5'9" (69 in) weighing 160 lb: BMI = 703 × 160 ÷ 69² = 112,480 ÷ 4,761 ≈ 23.6 — within the normal range.
The categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
What BMI doesn't tell you
BMI is a rough screen, not a diagnosis. It doesn't distinguish muscle from fat, so very athletic people can read "overweight" while being lean. It also doesn't account for age, sex, or where fat is stored. Treat it as one data point and talk to a doctor for the full picture.
Calculate body mass index.
Frequently asked questions
Is BMI accurate for athletes?
Not very. Muscle weighs more than fat, so muscular people often get a high BMI despite low body fat. Body-fat percentage is more useful for them.
What is a healthy BMI?
A BMI between 18.5 and 24.9 is considered the normal range for most adults.