BMI Calculator
Find your Body Mass Index and see which WHO weight category it falls into.
Last updated: June 18, 2026How is BMI calculated?
BMI is calculated by dividing your weight in kilograms by the square of your height in metres (kg/m²). In imperial units, multiply your weight in pounds by 703 and divide by height in inches squared. The result places adults into WHO categories from underweight to obese.
Units
kg
cm
Based on WHO BMI ranges for adults.
Formula
Examples
| Input | Result |
|---|---|
| Weight 70 kg, height 1.75 m | BMI 22.9 — normal weight |
| Weight 68 kg, height 1.65 m | BMI 25.0 — overweight (just over the threshold) |
| Weight 154 lb, height 69 in (5 ft 9 in) | BMI 22.7 — normal weight |
About this calculator
Body Mass Index (BMI) is a simple screening number that relates your weight to your height. It was developed in the 19th century by Adolphe Quetelet and is now used worldwide by clinicians and public-health bodies, including the World Health Organization (WHO), as a quick first-pass indicator of whether someone is at a healthy weight for their height.
The formula is straightforward. In metric units, BMI equals your weight in kilograms divided by the square of your height in metres (kg/m squared). In imperial units, BMI equals 703 multiplied by your weight in pounds, divided by the square of your height in inches. Squaring the height keeps the index roughly independent of how tall you are, so the same cut-off points apply to most adults.
To use this calculator, choose your unit system, then enter your height and your current weight. The tool instantly computes your BMI and places it in the matching WHO category. You can adjust the inputs to see how losing or gaining a few kilograms would change the result, which is useful for setting realistic goals.
Interpret the result using the standard WHO bands for adults: below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25.0 to 29.9 is overweight, and 30.0 or above is obese (further split into class 1, 2 and 3). A BMI of 22.9, for example, sits comfortably in the healthy range.
BMI has real limits. Because it uses only height and weight, it cannot tell muscle from fat, so very muscular athletes can read as overweight while older adults who have lost muscle can read as normal despite excess fat. It is also less reliable for pregnant women, children (who need age- and sex-specific charts) and some ethnic groups. Treat BMI as a starting point, not a diagnosis, and pair it with waist measurement and a clinician's advice.
Frequently asked questions
For most adults, a BMI between 18.5 and 24.9 is considered the healthy or normal range by the WHO. Below 18.5 is classed as underweight and 25 or above as overweight. These bands apply to both men and women aged roughly 20 and over.
The BMI formula and category cut-offs are identical for adult men and women. However, women naturally carry more body fat at the same BMI, so the number describes weight-for-height rather than body-fat percentage. For a fat-specific estimate, use a body-fat calculator.
BMI counts all your weight, including muscle, which is denser than fat. Athletes and people who lift weights can have a high BMI while carrying very little fat. In that situation, measures like waist circumference or body-fat percentage are more informative than BMI alone.
Not in the same way as for adults. Children and teens are assessed using age- and sex-specific BMI-for-age percentile charts rather than the fixed adult cut-offs, because their body composition changes rapidly as they grow. Always use a pediatric chart or a doctor for under-20s.
BMI only changes when your weight changes, since your height is fixed. A safe rate of loss is about 0.5 to 1 kg (1 to 2 lb) per week through a modest calorie deficit and activity. Rapid crash dieting may drop the number fast but often loses muscle and water rather than fat.
Sources & references
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