BMI Calculator
Calculate your Body Mass Index with WHO categories in metric or imperial units.
✓ Professional standard Uses internationally recognised clinical formulas — WHO, NHS, CDC, the U.S. Navy method and Mifflin-St Jeor — for screening-grade estimates.
BMI Calculator is a free online medical & health tool from Toolinza. Calculate your Body Mass Index with WHO categories in metric or imperial units. It runs entirely in your browser — your data is never uploaded — needs no signup, and works on any device. Toolinza offers 274+ free tools used by people across the UK, USA, Canada, Australia, the EU, India, Pakistan, the Middle East and worldwide.
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About the BMI Calculator
BMI, or Body Mass Index, is the number your doctor, gym and health app all reach for first — a quick estimate of whether your weight sits in a healthy range for your height. It takes just two measurements and gives an instant, internationally recognised category.
This BMI Calculator uses the World Health Organization classification and works in metric or imperial units. It is a useful screening figure and a good starting point for a conversation about your health — not a diagnosis, and best read alongside how you feel and other measurements.
How to use the BMI Calculator
- Choose metric or imperial units.
- Enter your height.
- Enter your weight.
- Read your BMI and its WHO category instantly.
Key features of the BMI Calculator
- Uses the WHO BMI classification
- Works in metric and imperial units
- Clear category ranges explained in plain language
- Instant result as you type
- Private — calculated in your browser
How the BMI Calculator works
This calculator applies standard, peer-reviewed formulas used by health professionals and public-health bodies worldwide. Depending on the metric, that includes the World Health Organization (WHO) classification, NHS and CDC guidance, the Mifflin-St Jeor equation for metabolic rate, and the U.S. Navy method for body composition. Inputs are converted between metric and imperial units using exact factors so results are consistent whichever system you use.
All calculations are performed in your browser, so the health information you enter is never sent anywhere.
Tips & best practices
- BMI does not distinguish muscle from fat, so very muscular people can read as "overweight" despite being lean — read it alongside body composition.
- Pair BMI with a waist measurement, which captures central fat and health risk that BMI alone misses.
- Track the trend over months rather than fixating on a single reading.
Standards & accuracy
Uses internationally recognised clinical formulas — WHO, NHS, CDC, the U.S. Navy method and Mifflin-St Jeor — for screening-grade estimates.
Important: these tools provide screening-grade estimates for general information and education only. They are not a medical diagnosis and do not replace professional advice. Always consult a qualified healthcare provider before making health decisions.
Who uses the BMI Calculator?
- A quick check of whether your weight is in a healthy range
- Tracking changes in weight over time
- A starting point before a check-up or health goal
- Educational use for students and trainers
Privacy & security
The BMI Calculator runs entirely inside your web browser. Your data — whether that is a file, figures or text — is processed on your own device and is never uploaded to a server, stored or shared. There is no signup and no account, so you can use it as often as you like while keeping full control of your information. This makes it a safe choice even for confidential and sensitive work.
Why choose Toolinza?
- 100% free — no hidden charges, watermarks or usage caps.
- Private & secure — your data stays on your device.
- Standards-compliant — accurate results suitable for the UK, USA, Canada, Australia, EU, India, Pakistan, the Middle East and worldwide.
- Works everywhere — desktop, tablet and mobile.
Frequently asked questions
For most adults the World Health Organization considers 18.5 to 24.9 a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese.
BMI is a useful screening tool but has limits. It does not separate muscle from fat, so it can misclassify very muscular people or older adults with low muscle mass. Use it with waist measurements and professional advice.
No. Children and teenagers are assessed using age- and sex-specific BMI percentile charts rather than the fixed adult categories, so interpret a young person's BMI with a healthcare provider.
Yes. The BMI Calculator is completely free with no signup, no watermarks and no usage limits. Toolinza is supported by unobtrusive advertising so every tool stays free.
Absolutely. This tool runs entirely in your browser — your data and files are never uploaded to any server, so everything stays private on your own device.
No. The BMI Calculator works instantly in any modern web browser on desktop, tablet and mobile — Windows, macOS, Linux, Android and iOS.