Free BMI Calculator Online

Body Mass Index is the single number doctors, gyms, life-insurance forms, and most fitness apps reach for first when they want a quick read on whether someone's weight is in a healthy range for their height. Our free online BMI calculator gives you that number in milliseconds — type your weight and height, switch between metric (kg/cm) and imperial (lbs/ft + inches) without retyping, and read off the WHO category instantly: underweight, normal, overweight, obese class I, II, or III. The colour-coded scale shows exactly where you fall and how far you are from the next category, so you can see whether a five-pound shift would actually move you across a threshold or just move you within the same band. Common situations people use it for: filling out a gym membership or insurance form that asks for BMI, tracking progress during a weight-loss or muscle-gain programme, sanity-checking a doctor's value at home, comparing yourself to public-health charts, and helping a parent monitor a teenager's growth. Important caveat that we put up front: BMI is a screening tool, not a diagnosis. It cannot tell apart muscle from fat, so a lean athlete and a sedentary person of the same height and weight will get the same score even though their body composition is completely different. Use it as a starting point and follow up with a healthcare professional for anything that matters medically. Pair this with our [Age Calculator](/tools/age-calculator) for life-event paperwork, the [Percentage Calculator](/tools/percentage-calculator) to track weight-change percentages over time, or the [Unit Converter](/tools/unit-converter) when you need to convert between cm and feet for non-BMI purposes.