BMI Calculator
Calculate body mass index and BMI category.
Body Measurements
Formula: BMI = weight in kg / height in metres².
About the BMI Calculator
The Body Mass Index (BMI) Calculator is a standardized tool designed to assess body weight relative to height. BMI serves as an epidemiological indicator to screen for potential weight-related health risks. It is calculated by dividing body weight in kilograms by the square of height in meters, or by using equivalent imperial conversions.
What the BMI Calculator Does
This tool accepts an individual's height and weight, computes their BMI score, and maps the result to official health classifications. It categorizes results into standard weight bands: underweight, normal weight, overweight, and three distinct classes of obesity. These categories provide a quick assessment of whether an individual's weight falls within a standard range for their height.
Significance and Context
BMI classifications are established under guidelines published by Health Canada and the World Health Organization (WHO). According to these official standards, adult weight categories are defined as follows:
- Underweight: BMI less than 18.5 (last verified July 10, 2026).
- Normal Weight: BMI from 18.5 to 24.9.
- Overweight: BMI from 25.0 to 29.9 (last verified July 10, 2026).
- Obese Class I: BMI from 30.0 to 34.9 (last verified July 10, 2026).
- Obese Class II: BMI from 35.0 to 39.9 (last verified July 10, 2026).
- Obese Class III: BMI of 40.0 or higher (last verified July 10, 2026).
While BMI is a widely utilized screening tool, it does not measure body fat percentage directly. It does not differentiate between fat mass and lean muscle mass. Consequently, individuals with high muscle density, such as athletes, may register elevated BMI scores without carrying excess body fat.
How to Use the BMI Calculator
To calculate BMI, the preferred measurement system (metric or imperial) is selected. For the metric system, height is entered in centimeters and weight is entered in kilograms. For the imperial system, height is entered in feet and inches, and weight is entered in pounds. The tool processes these inputs, displays the computed numerical BMI score, and identifies the corresponding health category according to Health Canada and WHO guidelines.
The BMI Calculator Formula
The calculation relies on the following standard formula:
Where: * weight is in kilograms * height is in meters For imperial units: BMI = [ weight (lbs) / (height (inches))^2 ] * 703 Explanation: Body Mass Index (BMI) is a standardized statistical measurement that estimates general body fat categories based on height and weight.
Step-by-Step Worked Example
Inputs: * Weight = 70 kg * Height = 1.75 meters Calculation: * Step 1: Calculate height squared = 1.75 * 1.75 = 3.0625 * Step 2: Divide weight by height squared = 70 / 3.0625 Result: * BMI = 22.86 What This Means: A BMI of 22.86 falls within the healthy weight range (18.5 to 24.9) for adults.
Frequently Asked Questions (FAQs)
❓ What are the official adult BMI categories?
According to the World Health Organization (WHO), adult BMI classifications are: Underweight (BMI under 18.5), Healthy weight (BMI 18.5 to 24.9), Overweight (BMI 25.0 to 29.9), and Obese (BMI 30.0 or higher).
❓ Is BMI a reliable measure of body fat?
BMI is a useful general screening tool but is not a direct measure of body fat. It does not distinguish between muscle mass and fat, meaning athletes or bodybuilders with high muscle mass may be classified as "overweight" or "obese" despite having low body fat.
❓ How does BMI calculation differ for children and teens?
While children's BMI is calculated using the same basic height/weight formula, their results must be plotted on a growth percentile chart that accounts for age and sex, since body fat composition shifts rapidly during developmental growth.
❓ What health risks are associated with a high BMI?
A consistently high BMI (in the obese range) is clinically linked to increased risks of chronic conditions, including cardiovascular disease, type 2 diabetes, high blood pressure, osteoarthritis, obstructive sleep apnea, and certain cancers.
❓ How can I lower my BMI safely?
To reduce your BMI safely, focus on a gradual weight loss of 1 to 2 pounds per week. Achieve this through a balanced, calorie-controlled diet rich in whole foods, coupled with regular physical exercise (at least 150 minutes of moderate activity weekly).