BMI Calculator

Body Mass Index (BMI) is a simple calculation that uses your height and weight to estimate whether you are in a healthy weight range. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is still widely used by healthcare providers as a quick screening tool.

The formula is straightforward: your weight in kilograms divided by your height in meters squared. A BMI between 18.5 and 24.9 is considered normal weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classified as obese.

While BMI is useful as a population-level health indicator, it has well-known limitations for individuals. It cannot distinguish between muscle and fat, so muscular people often register as overweight despite being very lean. It also does not account for fat distribution, which matters as much as total fat.

The standard BMI formula tends to underestimate body fat in shorter people and overestimate it in taller people. This is because it squares height, but the relationship between height and volume is actually cubic.

The New BMI formula, proposed by mathematician Nick Trefethen at Oxford University, corrects for this by using an exponent of 2.5 instead of 2. For people of average height both formulas give nearly identical results. The difference becomes noticeable if you are notably short or tall.

BMI is a useful starting point but should not be the only measure of your health. It does not account for muscle mass, bone density, age, gender, or ethnicity.

Athletes and people with high muscle mass will often have a high BMI despite low body fat. For a more complete picture, combine BMI with body fat percentage and waist circumference.

Is BMI accurate for athletes? Not particularly. BMI does not distinguish muscle from fat. Use body fat percentage instead for a better assessment.

Does BMI apply to children? Children and teens use BMI-for-age percentiles instead of standard adult categories. This calculator is designed for adults 18 and older.

What is a healthy BMI? The WHO defines 18.5 to 24.9 as normal weight. Some research suggests the lowest health risk may be in the 22 to 25 range.

Should I worry about my BMI? BMI is a screening tool, not a diagnosis. If yours is outside the normal range, discuss it with your doctor alongside other indicators like blood pressure and fitness level.