Health calculator
BMI Calculator
Estimate body mass index from height and weight for a quick health category check.
Quick answer
How do you calculate BMI?
Divide your weight in kilograms by your height in meters squared. In pounds and inches, multiply weight by 703 and divide by height in inches squared. A BMI of 18.5–24.9 is considered a healthy range for most adults.
BMI = weight (kg) / height (m)² • BMI = 703 × weight (lb) / height (in)²
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The BMI Calculator estimates body mass index from height and weight and places the result into a general health category.
About this BMI Calculator
Body Mass Index (BMI) is a quick screening number that compares your weight to your height. It is widely used by doctors as a starting point to flag potential weight categories from underweight to obese.
What you'll need
- • Height (cm/in/ft)
- • Weight (kg/lb)
- • Optional: age and sex for context
How it works
- 1. Convert height to meters and weight to kilograms.
- 2. Square the height value.
- 3. Divide weight by the squared height to get BMI.
- 4. Compare the result against standard categories: <18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese.
Worked example
A person who is 170 cm tall and weighs 70 kg has a BMI of 70 / (1.70 × 1.70) = 24.2, which falls in the normal range.
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BMI Calculator FAQ
What is the BMI Calculator?
The BMI Calculator is a free online tool that helps you estimate body mass index from height and weight for a quick health category check.
How do I use the BMI Calculator?
Open the BMI Calculator, enter the requested values, and review the instant estimate on the page.
Is the BMI Calculator free?
Yes. The BMI Calculator is free to use on Fast Online Calculator and does not require an account.
Is BMI accurate for athletes?
BMI does not separate fat from muscle, so very muscular people may show a high BMI without excess body fat. For athletes, body fat percentage is a more useful number.
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is classed as normal weight by the World Health Organization.
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