Free BMI Calculator
Body Mass Index from height and weight, in metric or US units.
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BMI
22.9
kg/m²
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Short answer
Body Mass Index (BMI) is body weight in kilograms divided by height in meters squared. The WHO classifies BMI under 18.5 as underweight, 18.5–24.9 as healthy, 25–29.9 as overweight, and 30+ as obese.
What is the BMI Calculator?
BMI is a screening statistic that estimates body fat from height and weight. It is not a diagnostic tool but is widely used by clinicians and health agencies as a starting point.
How does the BMI Calculator work?
Convert height to meters and square it. Divide weight in kilograms by the squared height. The result maps to a category defined by the World Health Organization.
Formula
Variables
BMIBody Mass IndexweightBody weight in kilogramsheightStanding height in meters
Explanation
For US units, BMI = 703 × weight(lb) / height(in)². The 703 constant converts pound-per-square-inch to kilogram-per-square-meter.
Examples
Example 1: 175 cm, 70 kg
BMI ≈ 22.9, in the healthy range.
Example 2: 5'10" (70 in), 180 lb
BMI ≈ 25.8, in the overweight range.
Applications
- Population health surveillance
- Initial clinical screening
- Fitness goal-setting
Advantages
- Simple to compute
- Consistent across studies
- No equipment beyond a scale and stadiometer
Limitations
- Does not distinguish muscle from fat — athletes may be misclassified
- Does not reflect fat distribution
- Cut-offs differ for some populations (e.g. Asian adults use lower thresholds)
Common mistakes
- Mixing metric and US inputs
- Interpreting BMI as body-fat percentage
Tips
- Pair BMI with waist circumference for a better metabolic risk picture
- Track BMI over time rather than a single reading
Related concepts
The BMI Calculator sits inside the Health Calculators hub, in the body composition cluster. What body mass is made of and how it is distributed. Understanding the terms below makes the output easier to interpret and easier to compare against neighbouring measures.
Practical use cases and industry applications
Understanding BMI
BMI is a screening statistic that estimates body fat from height and weight. It is not a diagnostic tool but is widely used by clinicians and health agencies as a starting point. Within health calculators, bmi belongs to the body composition cluster, where it shares terminology and assumptions with closely related tools.
Learning how bmi is calculated
For US units, BMI = 703 × weight(lb) / height(in)². The 703 constant converts pound-per-square-inch to kilogram-per-square-meter. Working through the variables one at a time — BMI, weight, height — makes the result reproducible by hand and easier to sanity-check.
Using bmi to make a decision
Population health surveillance Initial clinical screening Fitness goal-setting Because outputs depend on the assumptions you enter, run more than one scenario before committing to a figure.
How bmi compares with related measures
fat mass, lean mass, adiposity, percentile all describe adjacent aspects of body composition. Comparing this calculator's output against those measures — using the related tools listed on this page — prevents a single metric from being read in isolation.
Frequently asked questions
Is BMI accurate for muscular people?
No. Muscle is denser than fat, so bodybuilders and athletes often land in overweight or obese ranges despite low body fat.
What is a healthy BMI?
The WHO defines 18.5 to 24.9 as the healthy adult range.
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