BMI Calculator
Enter your weight and height to calculate your Body Mass Index (BMI) and see which category it falls into. This tool is for general information only and is not a substitute for medical advice.
How to use the BMI Calculator
Enter your weight in kilograms and your height in centimeters into the fields above, then click "Calculate." The tool instantly returns your BMI value along with the category it falls into — Underweight, Normal, Overweight, or Obese.
What is BMI?
Body Mass Index (BMI) is a simple calculation that uses your height and weight to estimate whether you're in a healthy weight range. It's calculated as weight (kg) divided by height (m) squared. BMI is widely used by doctors and health organizations as a quick screening tool, though it doesn't directly measure body fat and doesn't account for factors like muscle mass, bone density, age, or sex.
BMI categories
Below 18.5 — Underweight · 18.5–24.9 — Normal weight · 25–29.9 — Overweight · 30 and above — Obese
Frequently asked questions
Is BMI an accurate measure of health?
BMI is a useful general screening tool, but it has limitations. It doesn't distinguish between muscle and fat, so athletes and very muscular individuals may show a higher BMI despite having low body fat. It's best used as one data point alongside other health indicators, not as a standalone diagnosis.
Can I use pounds and inches instead of kg and cm?
This calculator currently accepts metric units (kilograms and centimeters). If you know your weight in pounds or height in inches, convert them first — 1 kg ≈ 2.2 lbs, and 1 inch = 2.54 cm.
Is this tool a substitute for medical advice?
No. This calculator is for general information only. For a full picture of your health, consult a doctor or qualified healthcare provider.
Is my data stored anywhere?
No. This tool is part of the Toolyard collection of free, browser-based utilities. Your weight and height are calculated locally in your browser and are never uploaded to or stored on a server.
What BMI does and doesn't tell you
Body Mass Index is a simple ratio of weight to height, and it's widely used because it's quick to calculate and correlates reasonably well with body fat levels across large populations. But BMI doesn't distinguish between muscle and fat — a muscular athlete can register as "overweight" by BMI despite having low body fat, and it doesn't account for where fat is distributed on the body, which matters for health risk assessment. It's a screening tool, not a diagnosis.
How the categories are defined
The standard adult BMI categories are: underweight (below 18.5), normal weight (18.5-24.9), overweight (25-29.9), and obese (30 and above). These thresholds were developed primarily from studies on adult populations and are generally not applied the same way to children, teenagers, pregnant women, or elderly adults, who typically need age- or context-specific assessment methods instead.
A note on using this responsibly
BMI is best used as one data point among several, not a standalone health verdict — waist circumference, body composition, activity level, and overall health markers give a fuller picture than BMI alone. If you have concerns about your weight or health, a healthcare provider can offer a more complete assessment than any online calculator.