How to Calculate BMI
Published 2026-07-14 · Updated 2026-07-14
BMI is a quick way to compare body weight with height. It is widely used as a screening number for adults, but it is not a full picture of body composition, fitness, or medical health.
BMI formula in pounds and inches
Use this formula: BMI = weight in pounds / height in inches squared x 703.
Height must be converted to total inches first. For example, 5 ft 9 in is 69 inches.
BMI example calculation
If someone weighs 170 lb and is 69 inches tall, the calculation is 170 / 69² x 703. The result is about 25.1.
That number is close to the border between the healthy weight and overweight BMI categories for adults.
How to interpret BMI
Adult BMI categories are commonly listed as under 18.5 for underweight, 18.5 to 24.9 for healthy weight, 25 to 29.9 for overweight, and 30 or higher for obesity.
BMI can be misleading for athletes, pregnant people, older adults, and anyone with a body composition that differs from the average. Use it as a starting point, not a diagnosis.
Quick Summary
BMI is calculated from height and weight. It is useful for a quick estimate, but personal health decisions should consider more than BMI alone.