BMI Calculator
Calculate your Body Mass Index (BMI) using metric (kg/cm) or imperial (lb/ft+in) units, with WHO weight category ranges.
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BMI is a general screening tool and is not a diagnosis. Consult a healthcare professional for personalized advice.
Body Mass Index (BMI) is a simple screening measure that uses your height and weight to estimate whether your weight falls into a healthy range. This calculator supports both metric (kilograms and centimeters) and imperial (pounds, feet and inches) units, and classifies your result using the World Health Organization's standard weight categories. Note that BMI is a general screening tool, not a diagnostic measure — it doesn't account for muscle mass, bone density, or body composition, so always discuss results with a healthcare professional.
How to use this calculator
- Select your preferred unit system: Metric (kg/cm) or Imperial (lb/ft+in).
- Enter your weight and height into the corresponding fields.
- Your BMI value and weight category update instantly as you type.
How BMI is calculated
Metric formula: BMI = weight (kg) / [height (m)]².
Imperial formula: BMI = 703 × weight (lb) / [height (in)]².
Both formulas produce the same BMI value for an equivalent height and weight — the 703 multiplier in the imperial formula simply converts pounds and inches into the metric-equivalent ratio.
Example: Metric calculation
Weight: 70 kg. Height: 175 cm (1.75 m).
BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9 — within the 'Normal weight' range.
Example: Imperial calculation
Weight: 154 lb. Height: 5 ft 9 in (69 in).
BMI = 703 × 154 / (69 × 69) = 108,262 / 4,761 = 22.7 — within the 'Normal weight' range.
Frequently asked questions
What are the WHO BMI weight categories?
Underweight: below 18.5. Normal weight: 18.5–24.9. Overweight: 25–29.9. Obese: 30 and above. These ranges apply to adults and are general population guidelines.
Is BMI accurate for everyone?
No. BMI doesn't distinguish between muscle and fat, so it can overestimate body fat in muscular individuals (such as athletes) and underestimate it in others. It's a screening tool, not a diagnosis, and results should be interpreted alongside other health indicators.
What's the difference between metric and imperial BMI calculation?
Both use the same underlying ratio of weight to height squared — the metric formula divides kilograms by meters squared, while the imperial formula divides pounds by inches squared and applies a 703 conversion factor to produce an equivalent result.
Is BMI different for children?
Yes. Children and teens are assessed using age- and sex-specific BMI percentile charts rather than the fixed adult categories used in this calculator, since healthy body composition changes significantly during growth.
Can BMI be used to diagnose health conditions?
No. BMI is a screening tool only. It cannot diagnose obesity-related conditions on its own and should not replace a full assessment by a healthcare professional.