BMI Calculator
This BMI calculator computes your Body Mass Index based on height and weight. Enter your measurements to instantly calculate your BMI score, see which health category you fall into (underweight, normal, overweight, or obese), and find your ideal weight range.
Body Mass Index Calculator
Enter your height and weight to calculate your BMI and see which category you fall into.
Frequently Asked Questions
What is BMI and how is it calculated?
BMI (Body Mass Index) is a numerical value calculated by dividing your weight in kilograms by the square of your height in meters (kg/m²). For imperial units, the formula is (weight in pounds × 703) ÷ (height in inches)². BMI provides a quick screening measure to categorize individuals into weight status categories such as underweight, normal weight, overweight, and obese.
What is a healthy BMI range?
A healthy BMI range is between 18.5 and 24.9, which is classified as "normal weight" by the World Health Organization (WHO). A BMI below 18.5 is considered underweight, 25.0 to 29.9 is overweight, and 30.0 or above is classified as obese. However, BMI is just one indicator of health and should be considered alongside other factors like body composition, waist circumference, and overall fitness.
Is BMI accurate for athletes and muscular people?
BMI can be misleading for athletes and muscular individuals because it does not distinguish between muscle mass and fat mass. Since muscle is denser than fat, a highly muscular person may have a high BMI despite having a low body fat percentage. For these individuals, other measurements like body fat percentage, waist-to-hip ratio, or DEXA scans provide a more accurate assessment of body composition.
What are the BMI categories?
The standard BMI categories defined by the WHO are: Underweight (below 18.5), Normal weight (18.5 to 24.9), Overweight (25.0 to 29.9), Obese Class I (30.0 to 34.9), Obese Class II (35.0 to 39.9), and Obese Class III or severe obesity (40.0 and above). These categories help healthcare providers assess potential health risks associated with weight.
How often should I check my BMI?
For most adults, checking your BMI once or twice a year is sufficient to monitor weight trends. If you are actively trying to lose or gain weight, checking monthly can help track progress. However, daily BMI checks are unnecessary since small weight fluctuations from water retention and food intake are normal and do not reflect meaningful changes in body composition.
Does BMI differ by age and gender?
Standard adult BMI categories apply equally to men and women aged 20 and older. However, women naturally carry more body fat than men at the same BMI. For children and teens aged 2 to 19, BMI is calculated the same way but interpreted using age- and gender-specific percentile charts because body composition changes significantly during growth and development.
What are the limitations of BMI?
BMI has several limitations: it does not account for muscle mass, bone density, or fat distribution. It may overestimate body fat in athletes and underestimate it in older adults who have lost muscle mass. BMI also does not consider ethnic differences in body composition or where fat is stored, as abdominal fat poses greater health risks than fat in other areas. For a comprehensive health assessment, BMI should be used alongside other measurements.
How to Calculate Your Body Mass Index (BMI)
What is BMI?
Body Mass Index (BMI) is a widely used screening measure that estimates body fat based on a person's height and weight. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and remains one of the most common tools used by healthcare professionals to assess whether an individual is at a healthy weight.
BMI provides a simple numeric value that places individuals into categories ranging from underweight to obese. While it does not directly measure body fat percentage, it serves as a useful starting point for health assessments and population-level studies.
How to Use This Calculator
- Select your preferred unit system: Imperial (feet, inches, pounds) or Metric (centimeters, kilograms).
- Enter your height using the appropriate fields.
- Enter your weight.
- Click "Calculate BMI" to see your result, category, and where you fall on the BMI scale.
- Use the copy button to save your results for future reference.
BMI Formula
The BMI formula divides weight by the square of height:
BMI = weight (kg) / height (m)²
For imperial units, the conversion is:
- Weight in kg = weight in lbs × 0.453592
- Height in meters = (feet × 12 + inches) × 0.0254
BMI Categories
The World Health Organization (WHO) defines the following BMI categories for adults:
| Category | BMI Range |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese Class I | 30.0 – 34.9 |
| Obese Class II | 35.0 – 39.9 |
| Obese Class III | ≥ 40.0 |
Examples
Example 1: Metric Calculation
A person who is 175 cm tall and weighs 70 kg:
BMI = 70 / (1.75)² = 70 / 3.0625 = 22.9 (Normal weight)
Example 2: Imperial Calculation
A person who is 5'10" (70 inches) and weighs 180 lbs:
Height in meters = 70 × 0.0254 = 1.778 m
Weight in kg = 180 × 0.453592 = 81.6 kg
BMI = 81.6 / (1.778)² = 81.6 / 3.161 = 25.8 (Overweight)
Use Cases
- Health Screening: Quickly assess whether your weight is within a healthy range during routine health checkups.
- Fitness Goals: Track your BMI over time as part of a weight management or fitness program.
- Population Studies: Researchers use BMI to study obesity trends and health outcomes across large groups.
- Insurance Assessments: Some insurers use BMI as one factor when evaluating health risk profiles.
- Clinical Reference: Healthcare providers use BMI alongside other metrics to evaluate overall health.
Tips and Limitations
While BMI is a useful screening tool, it has important limitations to keep in mind:
- BMI does not distinguish between muscle mass and fat mass. Athletes with high muscle mass may have a high BMI despite being lean.
- Age, gender, and ethnicity can influence the relationship between BMI and body fat.
- BMI is not recommended as the sole diagnostic tool for determining health status.
- For a more complete picture, consider combining BMI with waist circumference, body fat percentage, and other health indicators.
- Consult a healthcare professional for personalized health advice based on your individual circumstances.
BMI categories are designed for adults aged 20 and older. For children and teenagers, BMI is interpreted differently using age-specific and sex-specific percentile charts.