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U.S. BMI formula
When weight is in pounds and height is in inches, multiply weight by 703 and divide by height squared.
BMI = 703 × weight(lb) ÷ height(in)²
Worked example
At 150 lb and 65 in, BMI = 703 × 150 ÷ 65² ≈ 24.96.
What the number represents
BMI is a screening ratio of weight to height. It does not directly measure body fat, muscle mass or health status.
Common mistakes
- Using height in feet instead of total inches.
- Forgetting to square the height.
- Treating BMI as a diagnosis rather than a screening estimate.
Frequently asked questions
Why is 703 in the formula?
It is the conversion factor used when pounds and inches are substituted into the BMI relationship.
Should height be in inches?
Yes. Convert feet and inches to total inches first.
Is BMI the same as body-fat percentage?
No. They are different estimates.