BMI Calculator
Calculate your Body Mass Index from height and weight in metric or imperial units, and see your WHO weight category instantly.
🔒 Processed locally in your browser
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How to use
- Choose Metric (cm/kg) or Imperial (ft, in/lb) using the unit toggle at the top.
- Enter your height into the height field(s).
- Enter your weight into the weight field.
- Your BMI and weight category update instantly below — there's no button to press.
Features
- Supports both metric (cm/kg) and imperial (ft+in/lb) units
- Updates live as you type — no button to press
- Shows the standard WHO weight category alongside your BMI
- Validates input and shows a clear message instead of a broken result
- 100% client-side — your height and weight never leave your browser
Frequently asked questions
How is BMI calculated?
BMI = weight (kg) divided by height (m) squared. For imperial units, height and weight are first converted to metric using standard conversion factors before the same formula is applied.
Is BMI accurate for everyone?
Not perfectly. BMI is a simple screening measure and doesn't account for muscle mass, bone density, age, or sex. It can overestimate body fat in muscular people like athletes and underestimate it in older adults who've lost muscle mass. Treat it as a general indicator, not a diagnosis.
What are the BMI weight categories?
Using the WHO standard for adults: below 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is obese.
Does this tool store or upload my data?
No. All calculations happen locally in your browser. Your height and weight are never sent to a server or saved anywhere.
Can I use this for children?
No. This calculator uses adult BMI category thresholds. BMI for children and teens is assessed differently, using age- and sex-specific growth charts, so this tool isn't appropriate for them.