How to Calculate BMI (Formula & Examples)
How to calculate Body Mass Index in metric and imperial units, with the formula, worked examples and what the number means.
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Frequently asked questions
What is the BMI formula?
BMI = weight (kg) ÷ height (m)², or in US units 703 × weight (lb) ÷ height (in)².
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. 160 lb at 68 in is about 24.3.
What does the 703 factor do?
It converts the imperial calculation so it matches the metric BMI result based on kilograms and metres.
What BMI is considered healthy?
For adults, a BMI of 18.5 to 24.9 is the standard healthy-weight range used for screening.
Does BMI measure body fat?
No. It uses only height and weight, so it cannot distinguish muscle from fat — it is a screening estimate, not a body-fat measure.
Is calculating my own BMI enough?
It is a useful starting point, but for any health decision a professional can interpret it alongside other measures.
The BMI formula
Body mass index is weight divided by height squared. In metric units it is BMI = weight (kg) ÷ height (m)². In US units it is BMI = 703 × weight (lb) ÷ height (in)², the 703 factor converting pounds and inches to the metric result.
Worked example
Someone 5 ft 8 in (68 in) weighing 160 lb has a BMI of 703 × 160 ÷ 68² = 703 × 160 ÷ 4,624 ≈ 24.3. In metric, a person 1.75 m and 74 kg has 74 ÷ 1.75² = 74 ÷ 3.0625 ≈ 24.2.
Reading the result
The number maps onto the standard adult bands: under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight, and 30 or above obesity. These are screening categories for the general adult population.
BMI is quick and useful, but it only uses height and weight, so it cannot separate muscle from fat and may fit differently across ages and ethnic groups. Treat it as a general indicator and discuss any concerns with a healthcare professional.
Results are estimates for general guidance in United States and may not reflect the latest local rates, fees or rules. Check official sources before making decisions.