One BMI, two formulas
BMI itself has no units to convert — a BMI of 24 is 24 in every country. What changes is the formula you use to reach it. Type your numbers in either system and the other fills in, with the BMI worked out both ways.
Metric: kg ÷ m² · Imperial: 703 × lb ÷ in²
Common questions
Where does the 703 constant come from?
It's what makes the imperial formula (703 × lb ÷ in²) match the metric one (kg ÷ m²) exactly — it's the unit-conversion factor for pounds/inches² into kilograms/metres², not an independent measurement.
So do metric and imperial BMI ever actually disagree?
No — for the same person, both formulas give the same number, rounding aside. The 703 constant exists specifically so they always agree.
For general information only — not medical advice. Talk to a doctor about anything that concerns you.