BMI Calculator
How to calculate your BMI
Three quick steps from your height and weight to your BMI, category and healthy range.
Choose metric (centimetres and kilograms) or imperial (feet, inches and pounds). The form adapts so you only enter the measurements you actually use — no manual conversions needed.
Type your height and weight, then add your age and gender for context. You can also note an optional activity level — useful for interpreting a high BMI that may be muscle rather than fat.
Get your BMI score, weight category and healthy weight range, see your position on the visual BMI scale, and download a clean PDF report to keep or share with your doctor.
BMI Calculator — Free & Accurate
Body Mass Index, or BMI, is one of the most widely used measures in health screening. It compares your weight to your height to place you in one of four broad categories — underweight, normal weight, overweight or obese — and it does so with just two measurements that anyone can take at home. Our BMI calculator works in both metric and imperial units, shows your exact score, your category, and the weight range that would put you in the healthy zone for your height, all in a couple of seconds and entirely in your browser.
How BMI is calculated. The metric formula is your weight in kilograms divided by the square of your height in metres: BMI = kg ÷ m². If you measure in pounds and inches, the imperial version is 703 × pounds ÷ inches². As an example, someone who is 1.75 m (about 5 ft 9 in) tall and weighs 72 kg has a BMI of 72 ÷ (1.75 × 1.75) = 23.5, which sits comfortably inside the healthy range. The calculator handles the maths and the unit conversions for you, so you can compare a metric reading from a clinic with an imperial reading from a home scale without doing any arithmetic.
What the categories mean. For adults aged 20 and over, the World Health Organization defines a BMI below 18.5 as underweight, 18.5 to 24.9 as a healthy weight, 25 to 29.9 as overweight, and 30 or above as obese. These thresholds are the same for men and women. The healthy weight range this tool reports is simply the band of weights that would give you a BMI between 18.5 and 24.9 at your current height — a practical target range rather than a single "ideal" number, because a healthy weight is always a range, not a fixed figure.
Healthy weight ranges and what to do with them. Seeing your healthy range can be reassuring or motivating, but it is best treated as a guide rather than a rule. Weight that is distributed as muscle behaves very differently from weight stored as fat, and two people with the same BMI can have very different health profiles. If your result sits outside the healthy band, the calculator shows roughly how far away the nearest edge is, so you have a realistic sense of scale — but small, sustainable changes to everyday habits almost always beat dramatic short-term swings. A registered dietitian or your doctor can help you set goals that fit your body, your routine and any medical conditions you have.
Obesity, underweight and health risk. BMI matters because the extremes of the range are linked to real health outcomes. A consistently high BMI is associated with a greater risk of type 2 diabetes, high blood pressure, heart disease, joint problems and certain cancers, while being significantly underweight can mean a weakened immune system, reduced bone density, fertility problems and nutrient deficiencies. Importantly, these are statistical associations across large groups, not predictions about any one person. Where fat is stored — particularly around the waist — and your overall fitness, blood pressure, blood sugar and family history all shape your actual risk far more precisely than a single BMI number can.
Using BMI for fitness tracking. Because it is quick and free, BMI is a handy way to track a trend over weeks or months rather than to judge a single day. If you are working towards a goal, recording your BMI alongside other markers — waist measurement, resting heart rate, how your clothes fit, how much you can lift or how far you can run — gives a much richer picture than weight alone. Just remember that as you build muscle your BMI can rise even as your body composition improves, which is exactly why we let you add an activity level: a "high" BMI for a serious athlete means something very different from the same number for someone who is sedentary.
The limits of BMI. BMI was never designed to measure body fat, and it does not. It cannot tell muscle from fat, it ignores where fat is stored, and it does not account for age, bone density, pregnancy or ethnicity, all of which can shift what a "healthy" number looks like. For these reasons it works best as a first-pass screening tool that flags whether a closer look is worthwhile — not as a verdict. Pair it with a body fat measurement, a waist-to-height ratio, and a conversation with a healthcare professional for a complete and personalised assessment. Everything here runs locally on your device: your height, weight and other details are never uploaded or stored anywhere.
Why use this calculator?
More than a single number — a clear, visual, private read on where you stand.
Enter your height and weight and get your BMI, category and healthy weight range on screen at once — no sign-up, no waiting, no maths.
A clear underweight → normal → overweight → obese scale shows exactly where your number lands, so the result is intuitive at a glance.
Switch between US (ft-in/lbs), metric (cm/kg) and UK (stones & pounds) in one tap. Read a clinic measurement or a home-scale reading without converting anything by hand.
See the weight band that keeps your BMI healthy, how far the nearest edge is, and plain-English insights that put the number in context.
Download a clean, branded two-page report with your score, scale chart and health summary — easy to keep or hand to your doctor.
Everything runs in your browser. Your height, weight and personal details never leave your device or get sent anywhere.
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BMI is one piece of the picture — pair it with these to round it out.
Frequently asked questions
Short, practical answers to the questions people ask most about BMI.
BMI stands for Body Mass Index. It's a single number that relates your weight to your height to give a quick estimate of whether you are underweight, at a healthy weight, overweight or obese. Because it needs only two simple measurements, it's used all over the world for population health screening and as a starting point for individuals. It does not directly measure body fat — it's a proxy that works well on average but has clear limits for any one person.
In metric units, BMI is your weight in kilograms divided by the square of your height in metres (kg ÷ m²). In imperial units the equivalent is 703 × weight in pounds ÷ height in inches². For example, a person 1.75 m tall weighing 72 kg has a BMI of 72 ÷ (1.75 × 1.75) = 23.5. This calculator does the conversion and the maths for you in whichever units you choose.
For most adults aged 20 and over, a BMI between 18.5 and 24.9 is considered the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classed as obese. These thresholds come from the World Health Organization and are the same for men and women. The healthy weight range this tool shows is the band of weights that keeps your BMI in that 18.5–24.9 zone at your height.
BMI is a useful, fast screening tool, but it is not perfectly accurate for everyone. It cannot tell muscle from fat or show where fat is stored, so it can misclassify very muscular people, older adults, pregnant women and some ethnic groups. It's best read as a flag — a sign of whether a closer look is worthwhile — rather than a diagnosis. Pair it with a waist measurement, body-fat percentage and professional advice for a fuller, more personal assessment.
No. BMI uses only height and weight, so it has no way to separate muscle from fat. Muscle is denser than fat, which is why athletes and very muscular people often show a "high" BMI while carrying very little body fat. The reverse also happens: someone with a normal BMI can still have a high fat percentage and low muscle. That's the reason this calculator lets you add an activity level — it helps you interpret a high reading in context — and why a body-fat measurement gives a more complete picture.
Children and teenagers under 20 should not be assessed with the adult BMI categories. Their results are interpreted using age and sex specific BMI-for-age percentile charts, because healthy ranges shift constantly as they grow and differ between boys and girls. This calculator uses the adult WHO thresholds and is intended for adults aged 20 and over. For a child or teenager, please speak with a pediatrician or use a dedicated BMI-for-age tool.