What does BMI measure?
BMI expresses body weight relative to height squared. Common adult categories are below 18.5, 18.5 to below 25, 25 to below 30, and 30 or above. Clinical assessment also considers other measures and individual circumstances.
The BMI formula
Weight is converted to kilograms and height to metres, then weight is divided by height squared. Category boundaries use the unrounded result so display rounding does not change the classification.
How to use this calculator
- 1Select metric or imperial units.
- 2Enter current weight and height without shoes.
- 3Calculate and read the result alongside the limitations, not as a diagnosis.
Understanding your result
A BMI category is one piece of screening information. Muscle, fat distribution, age, ethnicity, and medical history can change its meaning. A clinician may consider waist size or other assessments instead of relying on BMI alone.
Assumptions & limitations
- Adult cutoffs are not intended for children, teens, or pregnancy; use age-specific clinical guidance.
- BMI cannot distinguish fat from muscle or show where body fat is stored.
Frequently asked questions
Can someone muscular have a high BMI?+
Yes. BMI includes all body mass, so substantial muscle can raise it without indicating the same body-fat level as another person with that BMI.
Is a BMI in the reference range proof of good health?+
No. BMI cannot assess diet quality, fitness, blood pressure, metabolic health, or fat distribution.
Do all populations use identical BMI risk thresholds?+
No. Some clinical guidance uses lower action thresholds for certain ethnic groups. The calculator displays the standard general adult categories.
Does switching units change my BMI?+
No. Equivalent metric and imperial measurements give the same result apart from small input-rounding differences.
