Body Mass Index, or BMI, is one of the most widely used screening tools for body weight. It's quick, free, and gives a rough sense of whether your weight is in a healthy range for your height. Here's what it means and how to work it out.
The BMI formula
BMI compares your weight to your height:
- Metric: BMI = weight (kg) ÷ height (m)²
- Imperial: BMI = 703 × weight (lb) ÷ height (in)²
For example, someone who is 1.75 m tall and weighs 70 kg has a BMI of 70 ÷ (1.75 × 1.75) ≈ 22.9.
Rather than doing the math by hand, you can use our BMI Calculator — just enter your height and weight (metric or imperial) and it shows your BMI and category instantly.
Standard BMI categories
For most adults, the World Health Organization ranges are:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
What BMI does not tell you
BMI is a useful starting point, but it has real limitations:
- It doesn't distinguish muscle from fat. Athletes with high muscle mass can register as "overweight" despite being very fit.
- It ignores fat distribution. Where you carry weight matters for health.
- It varies by age, sex and ethnicity. The standard ranges don't fit everyone equally.
Think of BMI as a quick flag, not a diagnosis. For a full picture, combine it with other measures and professional advice.
Track changes over time
BMI is most useful as a trend. Checking it occasionally as your weight changes tells you more than a single reading. Bookmark the BMI Calculator and recalculate whenever you want a quick check.
Related tools
If you're working on broader health and finance goals, you might also find these handy:
- Percentage Calculator — for tracking progress percentages
- Age Calculator — exact age in years, months and days
Disclaimer: BMI is a general screening tool and not a substitute for medical advice. Always consult a healthcare professional for personal health decisions.