Learn the BMI formula for metric and imperial units, walk through a worked example, and see the standard adult BMI categories.
Body Mass Index (BMI) is a quick screening number that relates your weight to your height. It’s widely used by doctors and health guidelines as a starting point for discussing weight-related health risks — not as a complete diagnosis on its own.
BMI is calculated the same way for adults regardless of sex or age, using metric units:
If you’re working in pounds and inches instead, the formula includes a conversion factor:
Take someone who weighs 70 kg and is 1.75 m tall:
Their BMI is approximately 22.9.
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
These ranges come from World Health Organization guidelines for adults and are a general reference point, not a personal medical assessment.
BMI only considers weight and height — it can’t distinguish muscle from fat. A very muscular person can show a high BMI while carrying little body fat, and BMI ranges aren’t designed for children, pregnant women, or older adults in the same way as for the general adult population. It’s best treated as a quick starting point, with more detailed measures used when a fuller picture is needed.
BMI Calculator
For most adults, a BMI between 18.5 and 24.9 falls into the “normal weight” range used by major health guidelines.
No. BMI is based only on weight and height, so it can’t tell the difference between muscle and fat, which is why very muscular individuals sometimes show a higher BMI than their body composition would suggest.
The BMI formula and the standard adult category ranges are the same for men and women. Individual health assessments may weigh other factors differently, but the calculation itself doesn’t change by sex.
There’s no fixed schedule — many people check it occasionally alongside other health measures rather than on a routine basis. A healthcare provider can advise on what makes sense for your situation.
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