BMI Calculator
Work out your Body Mass Index in metric or imperial units, with your weight category shown on a visual scale.
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How to Use the BMI Calculator
Enter your height and weight in metric or imperial units, then click Calculate. Your BMI score and health category appear instantly.
About This Tool
Body Mass Index (BMI) is a simple screening metric calculated by dividing weight (kg) by the square of height (m²). It was devised by Belgian mathematician Adolphe Quetelet in the 1830s and remains widely used by healthcare systems worldwide because it requires only two easily measured values. The WHO classifies BMI ranges as underweight (below 18.5), normal (18.5–24.9), overweight (25.0–29.9), and obese (30.0+).
However, BMI has significant limitations: it does not distinguish between muscle and fat, does not account for body composition differences related to age, sex, or ethnicity, and may overestimate body fat in athletes. This calculator supports both metric and imperial inputs and should be used as a screening tool alongside professional medical advice. Some medical forms also ask for exact age on a specific date — the find your precise age tool handles that calculation. For lifestyle goal-setting you might also compute percentage changes in weight over time.
Quick Reference Table
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese Class I |
| 35.0 – 39.9 | Obese Class II |
| 40.0 and above | Obese Class III |
Frequently Asked Questions
How is BMI calculated?
BMI is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight (kg) / height (m)². For imperial units, the formula is BMI = 703 × weight (lbs) / height (in)².
Is my health data safe?
Yes. The BMI Calculator runs entirely in your browser. Your weight and height are never sent to any server, stored in any database, or accessible to anyone but you.
How accurate is the BMI calculation?
The mathematical calculation is exact. However, BMI is a screening tool, not a diagnosis. It does not distinguish between muscle and fat, does not account for age or sex differences in body composition, and may overestimate body fat in athletes. Consult a healthcare provider for personal health advice.
Does the BMI Calculator have any usage limits or paid features?
No. The BMI Calculator is completely free with no limits, no signup, and no paid tier. Every metric (BMI, BMI Prime, Ponderal Index, ideal weight range) and the WHO classification table are available to everyone. Your height and weight values are computed locally in your browser and are never stored or transmitted.
Does BMI work for athletes or bodybuilders?
BMI often overestimates body fat in muscular individuals because it cannot distinguish between muscle mass and fat mass. A lean, muscular person may have a 'overweight' BMI while having low body fat. Body fat percentage, waist-to-hip ratio, or DEXA scans provide more accurate assessments for athletic individuals.
Created by The Toobits Team · Engineering & Editorial
Toobits is built, tested, and maintained by a small independent engineering team. Every tool is written in TypeScript, runs entirely in the browser, and is reviewed against its source formulas before publication.
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