BMI Calculator

Body mass index divides weight by height squared and returns a single number that is easy to compute and easy to misread. The arithmetic is trivial. The difficulty is in knowing what the number cannot say about muscle, fat distribution, age and population.

Weight in kilogramsBody weight. The formula wants kilograms, so convert first if you weigh in pounds.Height in centimetresStanding height, measured without shoes.

Body mass index

22.8571

Height converted to metres: 1.75
The same weight in pounds: 154.3236
Weight at the bottom of the healthy BMI range: 56.6563
Weight at the top of the healthy BMI range: 76.5625

Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.

The formula this calculator uses

BMI = weight in kilograms / (height in metres)^2

weight (kg): Body mass in kilograms
height (m): Standing height in metres, squared before dividing
BMI: Weight divided by height squared; effectively kilograms per square metre
703: Constant in the imperial form, BMI = 703 x lb / in^2

How to check the result by hand

1
Put height into the right unit
Metric needs metres, not centimetres, so 175 cm becomes 1.75 m. The imperial route needs inches. Dividing by a height still in centimetres inflates the squared value enormously, because the number being squared is a hundred times too large.
2
Square the height
1.75 squared is 3.0625. Squaring is the only non-obvious move, and it is what makes BMI sensitive to stature: a small change in height moves the index noticeably, because the effect is applied twice.
3
Divide weight by the squared height
70 / 3.0625 = 22.8571428571. On the imperial route, multiply the weight in pounds by 703 first, then divide by the squared height in inches; the two methods agree once rounding is set aside. Keeping the intermediate square at full precision avoids drift, and rounding only the final index keeps the imperial and metric answers aligned.
4
Read the result as a band, not a verdict
Locate the number against 18.5, 25 and 30, but treat the band as a screening signal drawn from populations rather than a statement about this particular individual.
5
Check what the number cannot see
Before drawing any conclusion, ask whether the person is muscular, where their fat sits, how old they are and which population the cut-offs came from. Each of these can change the meaning without changing the arithmetic; none of them changes the formula, but they change what the formula is allowed to conclude.

For worked examples, common mistakes and the limits of this formula, read the full How To Calculate BMI page.