Calculate your Body Mass Index. Supports metric and imperial units.
Calculating your Body Mass Index takes just seconds with our free online BMI calculator. Follow these steps to get your result instantly.
Body Mass Index (BMI) is a numerical value calculated from your height and weight. It is widely used by healthcare professionals as a screening tool to identify potential weight-related health risks. The BMI formula divides your weight in kilograms by the square of your height in meters.
The standard BMI categories defined by the World Health Organization (WHO) are as follows: Underweight (BMI below 18.5), Normal weight (BMI 18.5 to 24.9), Overweight (BMI 25 to 29.9), and Obese (BMI 30 and above). These categories apply to adults aged 18 and older.
The standard BMI calculation uses the same formula for both men and women. However, it is worth noting that women typically have more body fat than men at the same BMI, and older adults typically have more body fat than younger adults at the same BMI. For this reason, BMI is a screening tool and not a direct measure of body fatness or health.
While BMI is a useful and widely accepted screening tool, it has some limitations. Athletes and muscular individuals may have a high BMI due to muscle mass rather than fat. BMI may not accurately reflect health risks for elderly people who have lost muscle mass. It does not account for where fat is distributed in the body. A healthcare professional should always interpret BMI in context with other health indicators.
To maintain a healthy weight, the NHS and WHO recommend a balanced diet rich in fruits, vegetables, whole grains, and lean proteins, combined with regular physical activity of at least 150 minutes of moderate exercise per week. If your BMI indicates overweight or obesity, consulting a healthcare provider is recommended for personalized advice.
A healthy BMI for adults is between 18.5 and 24.9. A BMI below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is considered obese according to WHO guidelines.
BMI is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight (kg) ÷ height² (m). In imperial units, the formula is BMI = (weight in pounds × 703) ÷ height² (in inches).
BMI is less accurate for athletes and very muscular people because muscle weighs more than fat. A muscular athlete may have a high BMI despite being very healthy and having low body fat percentage.
The standard BMI calculator is designed for adults aged 18 and over. For children and teenagers, a different BMI-for-age calculation is used that accounts for age and gender-specific growth patterns.