Your Body Mass Index (BMI) is a simple measurement that uses your height and weight to estimate body fatness. It's not perfect, but it's a useful starting point for understanding whether you're in a healthy range.
The BMI Formula
For metric: BMI = Weight (kg) / Height (m) squared. Example: 70kg / 1.75m x 1.75m = 22.9.
For imperial: BMI = Weight (lbs) / Height (in) squared x 703. Example: 154lbs / 69in x 69in x 703 = 22.9.
Understanding BMI Categories
- Underweight: Below 18.5
- Normal weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obese: 30 and above
Note: These categories use WHO standards. China uses slightly different cutoffs, which our calculator handles automatically.
Finding Your Ideal Weight Range
For a given height, your ideal weight range corresponds to a BMI between 18.5 and 24.9. Multiply your height squared by 18.5 for the lower bound, and by 24.9 for the upper bound. This gives you a range, not a single number, because 'ideal' varies by muscle mass, frame size, and other factors.
Limits of BMI
BMI doesn't distinguish between muscle and fat. A muscular person might have a 'high' BMI despite low body fat. It also doesn't account for fat distribution. Use BMI as a screening tool, not a diagnosis. For a complete picture, consider waist circumference, body fat percentage, and how you feel overall.