BMI Calculator
Calculate your Body Mass Index from your weight and height, in metric or imperial units, and see which category you fall into.
Enter your weight and height to see the result.
How it works
BMI (Body Mass Index) relates your weight to your height to give a quick indication of whether you fall within a range generally considered healthy. The math is simple: your weight in kilograms divided by your height in meters squared. This tool also supports imperial units (pounds and inches), applying the standard 703 factor behind the scenes.
If you weigh 70 kg and are 1.75 m tall, the calculation is 70 divided by (1.75 × 1.75), which is about 22.9.
That number falls into one of the ranges defined by the World Health Organization:
- Below 18.5 — underweight
- 18.5 to 24.9 — normal weight
- 25 to 29.9 — overweight
- 30 to 34.9 — obesity class I
- 35 to 39.9 — obesity class II
- 40 or more — obesity class III
Enter your figures and the calculation happens instantly, without reloading the page.
When to use
BMI works well as a first screening: a cheap, immediate way to get a general sense of your weight relative to your height. That's why it shows up in routine checkups, public health campaigns and when tracking large groups of people.
Use it when you want a starting point — to decide whether it's worth talking to a doctor, to follow a trend over the months, or simply to understand where you sit relative to the reference ranges. It's more informative watched over time than as a single number on a single day.
Practical examples
Adult with normal weight
A person of 68 kg and 1.70 m has a BMI of 68 ÷ (1.70 × 1.70) = 68 ÷ 2.89 = 23.5. That places them in the normal-weight range (18.5 to 24.9), right in the middle of the healthy band.
Overweight range
Someone at 187 lb and 68 in lands around 28.4 in imperial units — within the overweight range. There, the number works as a nudge to look at habits and, if it makes sense, seek professional guidance.
Common mistakes
The most common mistake is treating BMI as a definitive diagnosis. It isn't. The index doesn't distinguish muscle from fat, doesn't consider how weight is distributed across the body, and doesn't account for age, sex or health history.
Because of that, athletes and very muscular people often show up as "overweight" even with low body fat — muscle is denser than fat and "weighs" in the calculation. At the other end, older adults who've lost muscle mass may have a normal BMI and still be at risk.
Another frequent slip is comparing your own BMI with someone else's as if it were a competition. The value makes more sense tracked in your own history, alongside other indicators like waist circumference, blood tests and a professional assessment.
Frequently asked questions
Is BMI accurate for athletes?
Not really. Since the calculation doesn't separate muscle from fat, people with a lot of muscle often fall into overweight or obese ranges without actually having excess fat. Body fat percentage is more appropriate in those cases.
What is a healthy BMI?
The range the WHO considers healthy runs from 18.5 to 24.9. But "ideal" varies from person to person: age, body composition and health conditions all matter. The reference is a starting point, not a rigid target.
Is BMI different for men and women?
The formula and WHO classification ranges are the same for both. The body-composition differences between the sexes are actually one of the limitations BMI can't capture on its own.
Can children use this calculator?
For children and teenagers, BMI is interpreted differently, using growth charts by age and sex. This calculator is designed for adults; for children, see a pediatrician.