Calculate your adult Body Mass Index using metric, US or UK units, then review the category, healthy-weight range and supporting measures behind the result.
Adult body mass index
Your BMI category, healthy-weight range and additional measures will appear after you calculate.
Methodology
BMI equals weight in kilograms divided by height in metres squared. For pounds and inches, the equivalent formula is weight in pounds divided by height in inches squared, multiplied by 703. The calculator converts every unit system to kilograms and metres, keeps full precision internally and rounds only the displayed result. Adult categories are applied to the unrounded BMI.
Worked example
An adult who weighs 70 kg and is 175 cm tall has a BMI of 70 ÷ 1.75² = 22.86, displayed as 22.9. That falls in the healthy-weight category. At 175 cm, the BMI 18.5–24.9 range corresponds to about 56.7–76.3 kg.
BMI guide
Body Mass Index is a height-to-weight ratio used to screen adult weight categories. The category describes where the number sits on a population scale; it does not describe your full health, fitness or body composition.
| BMI | Adult category | How the calculator labels it |
|---|---|---|
| Below 18.5 | Underweight | Underweight |
| 18.5 to 24.9 | Healthy weight | Healthy weight |
| 25.0 to 29.9 | Overweight | Overweight |
| 30.0 to 34.9 | Obesity | Obesity, Class 1 |
| 35.0 to 39.9 | Obesity | Obesity, Class 2 |
| 40.0 or higher | Obesity | Obesity, Class 3 |
Beyond the headline number
This reverses the BMI formula at your height using BMI 18.5 and 24.9. The difference to the nearest boundary is mathematical context, not a recommended weight-change plan.
BMI Prime is BMI divided by 25. A value of 1.00 sits at the upper boundary of the healthy adult range; 0.90 means the BMI is 90% of that boundary.
Ponderal Index divides weight in kilograms by height in metres cubed. It is displayed as a supplementary ratio and does not replace clinical assessment.
The category uses the unrounded result. A displayed BMI of 25.0 can therefore sit just below or above the exact boundary depending on hidden decimal places.
Limitations
Primary references
Related health tools
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Compare four reference-weight formulas and a BMI range.
Common questions
For most adults aged 20 and over, a BMI from 18.5 up to 25 is classified as healthy weight. A BMI below 18.5 is underweight, 25 to under 30 is overweight, and 30 or higher is obesity.
No. BMI uses only height and weight. It can be useful as a screening measure, but it does not directly measure body fat or separate fat from muscle, bone and other tissue.
No. People aged 2 to 19 are assessed with BMI-for-age percentiles that account for age and sex. This adult calculator uses fixed adult categories and is intended for ages 20 and over.
BMI can classify a muscular person in a higher category because it cannot tell muscle from fat. Waist measurement, health history and a professional assessment can add useful context.
This calculator is not designed to interpret weight during pregnancy. Ask a qualified healthcare professional about suitable weight monitoring before, during and after pregnancy.
BMI Prime compares your BMI with the upper healthy-weight boundary of 25. Ponderal Index is another height-and-weight ratio that uses height cubed and can provide extra context for very short or tall adults.
The adult categories are intended for people aged 20 and over. BMI can be less informative during pregnancy, for people with high muscle mass, and when a health condition changes height or body composition. Children and teenagers need BMI-for-age percentiles. Use the result as a screening estimate, not a diagnosis or a personal target. A qualified healthcare professional can interpret it alongside your health history and other measurements.