How this calculator works
Enter your weight and height (metric or imperial), and this calculator computes your BMI, tells you which WHO weight category you fall into, and shows the weight range that would put you in the “Normal” category at your height.
The formula
Metric: BMI = weight(kg) / height(m)² Imperial: BMI = 703 × weight(lb) / height(in)² Categories: Underweight (<18.5) · Normal (18.5–24.9) · Overweight (25–29.9) · Obese (30+)
Worked example
A person weighing 70kg at 1.75m tall:
- BMI = 70 ÷ (1.75 × 1.75) = 22.86, in the “Normal” category
BMI’s limitations
BMI is a screening tool, not a diagnosis. It doesn’t distinguish muscle from fat, doesn’t account for where fat is distributed on the body, and its category boundaries were developed primarily from population studies that may not reflect every individual’s ethnicity or body type equally well. Use it as one data point among several, not a standalone verdict on health.
Frequently asked questions (FAQ)
What is BMI and what does it measure?
BMI (Body Mass Index) is a simple ratio of weight to height, used as a rough population-level screening tool for weight categories. It doesn't directly measure body fat: it's a proxy that correlates with it on average, but not perfectly for any individual.
Is BMI accurate for athletes or muscular people?
Not really. BMI can't distinguish muscle from fat, so very muscular people (bodybuilders, many athletes) often show as "overweight" or "obese" by BMI despite having low body fat. For a fitness-focused estimate, our Body Fat calculator is more informative.
Does BMI account for age, sex, or ethnicity?
No. The standard BMI formula and WHO categories are the same for all adults regardless of age, sex, or ethnicity, even though body composition norms actually vary across these groups. This is one of BMI's most cited limitations.
What's a healthy weight range for my height?
This calculator shows the weight range where your BMI would fall between 18.5 and 24.9 (the WHO "Normal" range) at your entered height: a starting reference point, not a personalized target.
Is BMI the same as body fat percentage?
No. BMI is a weight-to-height ratio; body fat percentage is the actual proportion of your body that's fat tissue, typically estimated via circumference measurements (like our Navy method calculator), skinfold calipers, or scans. Two people with the same BMI can have very different body fat percentages.
Sources
This is a standard, public-domain formula (WHO BMI classification); no external source is needed beyond the widely published categories cited above.