BMI Calculator Calculators
Body mass index in metric or imperial, with the standard categories.
BMI Calculator is a free online tool that body mass index in metric or imperial, with the standard categories. It runs entirely in your web browser using plain JavaScript, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Calculators
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- plain JavaScript
- Settings
- 3
- Works offline
- Yes, after the first visit
About BMI Calculator
BMI is a rough population-level screen, not a diagnosis. It takes no account of muscle mass, bone density, body composition or age, so athletes routinely read as “overweight” while being nothing of the sort.
How to use it
- Enter units, weight and height.
- Results update the moment anything changes.
The 3 settings
| Setting | What it does | Default |
|---|---|---|
| Units | Choose from 2: Metric (kg, cm), Imperial (lb, in). | Metric (kg, cm) |
| Weight | A numeric value. | 75 |
| Height | A numeric value. | 175 |
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
| Controls | Units, Weight, Height |
Questions
Is BMI actually reliable?
As a population-level screen, reasonably. For an individual, poorly. It knows nothing about muscle mass, bone density, body composition, age or ancestry — which is why well-trained athletes routinely score as "overweight".
Where do the categories come from?
The WHO thresholds: under 18.5, 18.5–24.9, 25–29.9, and 30+ split into three obesity classes. Some health bodies apply lower thresholds for people of South Asian descent, where cardiometabolic risk rises earlier.
What is a better measure?
Waist-to-height ratio predicts cardiometabolic risk better than BMI and needs only a tape measure — keep it under half your height. Body fat percentage is better still if you can measure it properly.