Free online tool
BMI Calculator
Calculate your Body Mass Index in metric or imperial units and see which WHO category it falls into.
What BMI measures — and what it doesn't
Body Mass Index is a simple ratio of weight to height, calculated as kilograms divided by height in metres squared. It's widely used as a population-level indicator of whether someone is under-, normal-, over- or obese-weight. It's a rough screening tool — it doesn't distinguish between muscle and fat, doesn't account for body composition, age or ethnicity, and can misclassify athletes with high muscle mass.
How to interpret your result
The WHO categories are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese. Treat your number as one data point among many. If you're concerned about your weight or health, talk to a doctor — they'll consider your full picture, not just a single ratio.
+Is BMI accurate for athletes?
Not really. A muscular athlete can have a BMI in the 'overweight' range while having low body fat. Body-fat percentage is a better indicator for very active people.
+Is my data private?
Yes. Everything runs in your browser. Nothing is sent, stored or logged.
Why use the BMI Calculator on ToolNest?
The BMI Calculator is one of more than forty free browser-based utilities we maintain on ToolNest. Every tool on the site is engineered around the same three promises: it must be fast, it must protect your privacy, and it must be genuinely useful without hiding features behind an account, a paywall, or an email capture form. Whether you use the BMI Calculatoronce a month or several times a day, it should feel like a native part of your workflow — open the tab, get the result, move on.
Everything happens directly inside your web browser. When you type, paste, or upload something into the BMI Calculator, that data never leaves your device. There is no server round-trip, no logging, no analytics pixel watching your keystrokes, and no third-party API silently receiving a copy of your input. Closing the browser tab is the same as clearing your session. This is a deliberate design choice: too many free "online tools" quietly funnel user content through remote servers, and we do not think a utility as small as this one justifies that risk.
Speed is the other pillar. The BMI Calculator loads on a cold connection in well under a second and stays responsive on older phones, low-power laptops, and metered mobile networks. There are no heavy frameworks layered on top of the tool, no autoplay video ads, and no blocking third-party scripts. Search engines like Google reward pages that load quickly and stay interactive, but more importantly, so do human visitors who came here to get one specific job done.
If the BMI Calculator saves you time, the best thing you can do is bookmark this page and share it with a colleague or classmate who might need it. We also welcome direct feedback — bug reports, feature requests, and suggestions for entirely new tools all go to the same inbox and are read by a human. The best tools on ToolNest started life as a one-line reader email, and this page will keep improving as long as people keep telling us what they wish it did better.