BMI Calculator
Body Mass Index is a quick screen for whether your weight is in a healthy range for your height. This calculator works in both metric and imperial units and shows the WHO weight category your BMI falls into.
How to use the BMI Calculator
- Enter your inputs into the BMI Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The BMI formula
BMI = weight (kg) / height (m)²
In imperial units, BMI = (weight in lb / height in in²) × 703. BMI is unitless and applies to adults aged 20+. The standard WHO categories are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese.
Worked example
An adult who is 1.75 m tall and weighs 70 kg has a BMI of 70 / (1.75 × 1.75) ≈ 22.9 — within the normal range. A 5'9", 180 lb adult has BMI = (180 / 69²) × 703 ≈ 26.6 — into the overweight range.
Frequently asked questions
What is a healthy BMI for adults?
The WHO classifies a BMI of 18.5 to 24.9 as normal weight for adults. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classified as obese.
Is BMI accurate for athletes?
BMI can overestimate body fat in muscular individuals because muscle is denser than fat. Athletes and bodybuilders with high muscle mass may have a BMI in the overweight range despite low body fat — use a body fat or lean body mass calculator for a fuller picture.
Does BMI work for children?
Adult BMI categories do not apply to children and teens. For people under 20, BMI is interpreted using age- and sex-specific percentile charts from the CDC.
What are the limitations of BMI?
BMI is a screening tool, not a diagnostic. It does not measure body composition, fat distribution, or muscle mass, and it can misclassify athletic or elderly people. Pair it with body fat percentage or waist-to-hip ratio for a complete view.