BMI Calculator

Body Mass Index (BMI) is a numerical screening value calculated by dividing your weight in kilograms by the square of your height in meters. The formula — BMI = weight (kg) ÷ height (m)² — was developed in the 19th century by Belgian mathematician Adolphe Quetelet and remains one of the most widely used population-level health indicators in modern medicine.

The World Health Organization classifies BMI into four standard ranges: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), and obese (30.0 and above). Each band correlates statistically with different long-term health risks, including cardiovascular disease, type 2 diabetes, hypertension, and certain cancers.

BMI is a screening tool, not a diagnosis. Athletes with high muscle mass can register as overweight despite low body fat, and older adults may show normal BMI while carrying elevated visceral fat. For a more complete view of body composition, pair BMI with body fat percentage, waist-to-height ratio, and lean mass measurements.

Doctors, dietitians, school nutrition programs, military fitness assessments, insurance underwriters, and corporate wellness initiatives all use BMI as an entry-level health metric. It is fast, requires no equipment, and produces a comparable number across populations — which is why it remains the default starting point in clinical screening.

Tracking BMI over time is more informative than a single reading. A gradual upward trend, even within the healthy range, can flag lifestyle drift before it becomes a clinical issue. Calculate your BMI quarterly, log it alongside resting heart rate and waist circumference, and discuss meaningful changes with a qualified clinician.

Enter your height in centimeters or switch to feet-and-inches for imperial units. The calculator handles both measurement systems internally and automatically converts to metric to apply the standard BMI formula. Then enter your weight in kilograms or pounds depending on your selected unit system.

The result panel shows your BMI value, the WHO classification band, and a color-coded indicator. The healthy range is green; underweight, overweight, and obese ranges are flagged so you can see at a glance which side of the spectrum you fall on. Hover or tap any band to read the underlying definition.

For accurate results, measure your height without shoes against a flat wall and weigh yourself in the morning before eating, on a calibrated scale, ideally on the same scale at the same time of day for repeat measurements. Daily fluctuations of 1–2 kg are normal due to hydration and meal timing, so trust weekly averages over single readings.

If your BMI falls outside the healthy range, use it as a prompt to investigate further rather than as a final verdict. Combine it with body fat percentage, waist circumference, blood pressure, and lipid panel results when discussing health goals with your doctor. The calculator is a starting point — your full health picture requires more than a single number.