BMI Calculator
Calculate your Body Mass Index using metric or imperial units. Includes WHO category interpretation.
Body Mass Index (BMI) is the most widely used screening number in health and fitness — it appears on doctor's forms, insurance charts, and fitness apps everywhere. This calculator computes your BMI from your height and weight in either metric or imperial units and places you in the standard World Health Organization category, from underweight through the obesity ranges, with a plain-language interpretation of what that means.
BMI is popular because it is fast, free, and requires no equipment beyond a scale and a tape measure. It gives a useful at-a-glance estimate of whether your weight falls in a range associated with lower health risk for the general population. That said, it is a starting point and not a diagnosis — it cannot tell muscle from fat — so this page also explains where the number is helpful and where it falls short, so you can interpret your result sensibly rather than treat it as a verdict.
Plug in some numbers —
we'll crunch.
How to use
- 1Select your preferred unit system — metric (kg/cm) or imperial (lbs/inches).
- 2Enter your current weight.
- 3Enter your height.
- 4Click Calculate to see your BMI and category.
How it works
BMI is a single ratio: your weight in kilograms divided by the square of your height in meters (kg/m²). In imperial units the formula is weight in pounds × 703 ÷ height in inches squared, which converts to the same number. Squaring the height is what lets one threshold apply to people of different sizes, since mass tends to scale roughly with the square of height in adults.
The WHO categories are: under 18.5 is underweight, 18.5–24.9 is the normal range, 25–29.9 is overweight, and 30 or above is obese. These cut-offs were derived from population data linking BMI to health outcomes. Crucially, the formula uses only height and weight — it has no information about body composition, age, sex, or fat distribution, which is the source of both its convenience and its limitations.
Worked examples
A metric calculation
You are 1.75 m tall and weigh 72 kg.
- Square your height: 1.75 × 1.75 = 3.0625.
- Divide weight by that: 72 ÷ 3.0625 = 23.5.
Your BMI is 23.5, which sits comfortably in the normal-weight range (18.5–24.9). It suggests your weight is in a healthy band for your height — though it says nothing about your fitness or body composition.
Where BMI misleads — the athlete
A 1.85 m, 95 kg strength athlete with 10% body fat.
- Height squared: 1.85 × 1.85 = 3.4225.
- BMI = 95 ÷ 3.4225 = 27.8.
The formula labels this very lean athlete 'overweight' at 27.8, purely because muscle is dense and BMI cannot see it. This is the classic case where BMI alone gives the wrong impression.
Tips & common mistakes
Treat BMI as a screening tool, not a diagnosis. Its biggest blind spot is that it cannot distinguish muscle from fat: very muscular people are often misclassified as overweight, while someone with low muscle and high abdominal fat can score 'normal' yet carry real health risk. Pair BMI with a measure of body composition or a simple waist measurement for a fuller picture.
Context changes the meaning of the number. Older adults naturally lose muscle, and some populations (notably people of South and East Asian descent) face elevated metabolic risk at BMIs that look normal by Western thresholds. BMI is also temporarily meaningless during pregnancy. If your result falls near a category boundary, do not over-react to a single point.
Where BMI is most useful is at the extremes and as a trend over time — a steadily rising or very high figure is a genuine signal worth acting on. Use it as a prompt to look deeper, not as the final word. This calculator is for general information only and is not medical advice; discuss any health concerns and your full risk profile with a qualified healthcare professional.
Frequently asked questions
⚠ BMI is a screening tool, not a diagnostic measure. Consult a healthcare professional for personalized advice.
Last reviewed: June 2026
About this calculator
Calculate your Body Mass Index using metric or imperial units. Includes WHO category interpretation.