BMI Calculator
Calculate your Body Mass Index (BMI) using metric (kg/cm) or imperial (lbs/inches) measurements. Instantly see your WHO weight category. Free, private, and runs entirely in your browser with no uploads.
Key Capabilities
Metric and imperial unit support
Enter weight in kilograms or pounds and height in centimetres or feet and inches. The calculator converts internally — no manual unit conversion required.
WHO adult classification with visual indicator
Results display your BMI alongside the WHO category — Underweight, Normal weight, Overweight, or Obese — with a colour-coded visual indicator showing where you fall on the clinical scale.
Entirely browser-based, zero data retention
All arithmetic runs locally in your browser via JavaScript. Your weight and height values are never transmitted to any server, logged, or associated with your identity.
How to Use
Select your unit system
Toggle between metric (kg and cm) and imperial (lbs and ft/in) using the selector at the top.
Enter weight and height
Type your values — the BMI result updates automatically as you type, no submit button needed.
Read your WHO category
Review the BMI number and category label. Consult your GP to discuss what the result means in the context of your full health picture.
Common Use Cases
- Pre-appointment health screeningA patient preparing for a GP annual check-up calculates BMI at home to understand how their weight will be discussed and what lifestyle recommendations to expect, arriving informed.
- Corporate wellness programme coordinatorsAn HR team running a workplace health initiative points employees to the tool for private self-assessment without collecting sensitive biometric data centrally.
- Dietitians tracking client progressA dietitian asks clients to recalculate BMI between sessions as a quick reference point alongside more detailed body composition measurements like DEXA or bioimpedance.
Frequently Asked Questions
What is BMI?
Body Mass Index (BMI) is a value derived from a person's weight and height. It is used as a screening tool to categorise adults as underweight, normal weight, overweight, or obese. BMI does not directly measure body fat.
What are the WHO BMI categories?
Underweight: BMI below 18.5. Normal weight: 18.5–24.9. Overweight: 25–29.9. Obese: 30 or above. These classifications apply to adults aged 18 and over.
Is BMI accurate for everyone?
BMI is a useful population-level screening tool but has known limitations. It does not account for muscle mass, bone density, age, sex, or fat distribution. Athletes may show high BMI due to muscle. Always consult a doctor for a comprehensive health assessment.
Is my data private?
Yes. All BMI calculations run locally in your browser using JavaScript. No personal data, weight, or height values are ever sent to any server.
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