BMI Calculator
Calculate body mass index from height and weight.
BMI categories follow the World Health Organization (WHO) classification: under 18.5 underweight · 18.5–24.9 normal · 25–29.9 overweight · 30+ obese. BMI is a general guide and doesn't account for muscle mass, age, or body composition. Source: WHO ↗
Use on any page (bookmarklet)
Want BMI Calculator without leaving the page you're on? Drag the button below to your bookmarks bar, then click it on any website to open BMI Calculator right there — it runs entirely in your browser.
Use responsibly: a bookmarklet runs on whatever page you click it on. Avoid sensitive sites such as online banking, payment, or healthcare pages — you run it at your own risk. Everything is processed locally and no data is sent anywhere. See our Terms.
- Show your bookmarks bar if it's hidden — Ctrl+Shift+B (⌘+Shift+B on Mac).
- Drag the button above onto the bookmarks bar.
- Open any website and click the bookmark — the BMI Calculator panel appears in the top-right corner. Use ✛ to move it between corners, or ›/‹ to tuck it against the edge and pull it back out.
- Click the bookmark again (or the ✕) to close it.
Note: a few sites with strict security policies may block bookmarklets.
Examples
70 kg, 175 cm
Input
Metric
Output
BMI 22.9 · Normal weight
154 lb, 5 ft 9 in
Input
Imperial
Output
BMI 22.7 · Normal weight
About this tool
This free online BMI calculator works out your Body Mass Index from your height and weight, in metric or imperial units, and shows which WHO category it falls into. The result updates instantly as you type, and everything runs in your browser with no upload.
How to use
- Choose metric (kg, cm) or imperial (lb, ft/in).
- Enter your weight and height.
- Read your BMI and category below.
Good to know
BMI is a quick screening number, not a diagnosis. It doesn't measure body fat directly or account for muscle, bone, age, or sex — so use it as a starting point and talk to a healthcare professional for personal advice.
Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). In imperial units it's 703 × pounds ÷ inches². This calculator does both for you.
Is this BMI calculator free?
Yes — it's a completely free online BMI calculator with metric and imperial units and no sign-up.
What are the BMI categories?
Using WHO ranges: below 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is obese.
Where do these BMI ranges come from?
The category cut-offs come from the World Health Organization (WHO) classification of body mass index for adults. A source link to the WHO is shown beneath the result. Note that some countries and clinicians use slightly different thresholds, especially for certain populations.
Can I use pounds and feet/inches?
Yes. Switch to Imperial to enter weight in pounds and height in feet and inches.
Is BMI accurate for everyone?
BMI is a general screening tool. It doesn't distinguish muscle from fat or account for age, sex, and body composition, so athletes and some groups may get misleading numbers. Treat it as a rough guide.
Is my health data uploaded anywhere?
No. The calculation runs entirely in your browser with no upload, so your measurements stay private.
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