BMI Calculator
Calculate your Body Mass Index instantly.
How this calculator works
Formula
BMI = weight (kg) / height (m)²
Method
The Quetelet index — a quick screen for weight relative to height. Not a diagnostic.
Example
A 175 cm, 70 kg adult has a BMI of 22.9 — the normal range.
The complete guide to the BMI Calculator
The BMI calculator is a quick screen for weight relative to height. It's used by clinicians as a first-pass indicator of underweight, healthy, overweight, and obese ranges — but the number always needs context. Here's exactly what it means and where it falls short.
How BMI is calculated
BMI = weight in kilograms divided by height in meters squared. In imperial units, multiply lbs / (inches × inches) by 703. A 175 cm, 70 kg adult has a BMI of 22.9, which lands in the normal-weight band.
The standard categories
Under 18.5 is underweight. 18.5 to 24.9 is normal. 25.0 to 29.9 is overweight. 30 and above is obese, further split into class I (30–34.9), II (35–39.9), and III (40+). These cut-offs come from World Health Organization population studies linking BMI to disease risk.
Where BMI misleads
Muscle is denser than fat, so athletes routinely score overweight despite low body-fat percentages. Older adults may fall in the healthy range while carrying too little muscle (sarcopenia). Kids and teens need age-and-sex-specific percentiles; pregnant women shouldn't use BMI at all.
A better companion measurement
Pair BMI with waist circumference. Waist above 102 cm in men or 88 cm in women signals central obesity that carries metabolic risk even at a normal BMI.
What to actually do with a BMI number
Treat it as a screening result, not a diagnosis. If you're outside the normal band and want to change it, focus on trend (monthly averages), not the daily bathroom-scale swing. Weight moves 1–2 kg with hydration alone.
Ethnic and regional adjustments
Some populations, notably South and East Asian, carry health risks at lower BMIs. Many guidelines recommend using 23 as the overweight threshold for these groups. Ask a clinician what applies to you.
Using the calculator
Switch between metric and imperial with the toggle. The result updates instantly. Use it before and after a training block to sanity-check your direction, but rely on body-composition tools for the fine detail.
Frequently asked questions
Is BMI accurate for muscular people?
No. Consider body-fat percentage tools like the Navy method calculator instead, or a DEXA scan for a definitive number.
What BMI is 'healthy'?
18.5 to 24.9 for most adults. Consult a clinician for personal context.
Can I use this during pregnancy?
No. Standard BMI doesn't apply during pregnancy.