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BMI Calculator

Calculate your Body Mass Index instantly with our free BMI calculator. Supports metric and imperial units, shows BMI category, healthy weight range, and a visual BMI scale.

Last Updated: May 2026

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How to Use the BMI Calculator

  1. 1

    Choose Your Unit System

    Select Metric (kg and cm) or Imperial (pounds and feet/inches) using the toggle at the top of the calculator.

  2. 2

    Enter Your Weight and Height

    Type in your current weight and height. For imperial, enter feet and inches separately.

  3. 3

    Click 'Calculate BMI'

    Your BMI score, category (Underweight / Healthy / Overweight / Obese), and healthy weight range for your height will appear instantly.

What Is BMI?

Body Mass Index (BMI) is a numerical value derived from a person's weight and height. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and has been used by healthcare professionals as a quick screening tool for weight-related health risks ever since. A BMI calculatordivides your weight in kilograms by the square of your height in meters. While BMI doesn't directly measure body fat, research consistently shows that it correlates with direct body fat measurements in most people. The World Health Organization and the CDC use BMI as a standard population-level health indicator.

BMI Categories — WHO Classification

BMI RangeCategoryHealth Risk
Below 18.5UnderweightIncreased risk (nutritional deficiency)
18.5 – 24.9Healthy WeightMinimal risk
25.0 – 29.9OverweightIncreased risk
30.0 – 34.9Obese Class IHigh risk
35.0 – 39.9Obese Class IIVery high risk
40.0 and aboveObese Class IIIExtremely high risk

BMI Limitations — Important to Know

BMI does not account for muscle mass, bone density, age, sex, or ethnic differences. Athletes may have a high BMI with low body fat. The elderly may have a normal BMI with high body fat. Always use BMI alongside other health assessments. This tool is for informational purposes only and does not constitute medical advice.

Frequently Asked Questions

What is a healthy BMI range?

A healthy BMI is between 18.5 and 24.9 for most adults. Under 18.5 is considered underweight; 25–29.9 is overweight; 30 and above is obese. These are general guidelines from the World Health Organization (WHO) and may vary for different ethnic groups and body types.

Is BMI accurate for athletes and muscular people?

No — BMI is not accurate for highly muscular individuals. Because muscle is denser than fat, athletes often have a high BMI despite having low body fat. For this reason, BMI should be used as a screening tool only, not a diagnosis. Body fat percentage, waist circumference, and other measures provide a more complete picture.

What is the BMI formula?

The BMI formula is: BMI = weight (kg) ÷ height² (m²). In imperial units: BMI = 703 × weight (lbs) ÷ height² (inches²). For example, a person weighing 70 kg at 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

What is the difference between BMI and body fat percentage?

BMI is a simple ratio of weight to height and does not directly measure fat. Body fat percentage measures the actual proportion of your body that is fat tissue. Body fat percentage is more accurate but requires special equipment (DEXA scan, skinfold calipers, or bioelectrical impedance). BMI is useful for population-level screening because it only requires weight and height.

Is BMI calculated differently for children?

Yes — for children and teens aged 2–19, BMI is calculated using the same formula but then compared to age- and sex-specific percentile charts (called BMI-for-age). A child is considered underweight below the 5th percentile and obese at or above the 95th percentile.

What BMI is considered obese?

A BMI of 30 or above is classified as obese by the World Health Organization. Obesity is further divided into Class 1 (30–34.9), Class 2 (35–39.9), and Class 3 or severe obesity (40+). If your BMI is in the obese range, consult a healthcare professional for a comprehensive evaluation.

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