About the BMI Calculator
A BMI (Body Mass Index) calculator is a screening tool that compares weight to height to categorize body size. It is widely used by clinicians and public health agencies as a first-pass indicator of possible weight-related health risk.
How it works
- Measure height and weight. Use consistent units (metric or US). The calculator converts internally.
- Apply the BMI formula. Weight in kilograms divided by the square of height in meters.
- Match to the category table. Under 18.5 is underweight, 18.5–24.9 is normal, 25–29.9 is overweight, 30 and above is obese.
Formula
- weight = Body mass in kilograms
- height = Height in meters
Frequently asked questions
What is a healthy BMI?
The World Health Organization defines a normal adult BMI as 18.5 to 24.9. This range is a population-level guideline and does not account for muscle mass, frame size, or ethnicity.
Is BMI accurate for athletes?
BMI can overestimate body fat in muscular individuals because muscle is denser than fat. Body-fat percentage or waist-to-hip ratio are often more informative for athletes.
How is BMI used clinically?
BMI is a screening tool, not a diagnosis. Clinicians use it alongside blood pressure, blood work, and waist circumference to evaluate cardiovascular and metabolic risk.
Why does BMI differ for children?
For children and teens, BMI is interpreted via CDC growth-chart percentiles rather than fixed categories, because healthy BMI changes with age and sex during development.
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Concepts
Sources & methodology
- Category thresholds follow the WHO and CDC adult BMI classification.