About this tool
This BMI calculator works out body mass index from your height and weight, in centimeters and kilograms or in feet, inches, and pounds, and places the result on the World Health Organization scale: underweight (with its three sub-classes), normal weight, overweight, and obesity classes I, II, and III. Alongside the number it shows the healthy weight range for your exact height (the weights that correspond to a BMI of 18.5 to 24.9), how many kilograms or pounds separate you from that range if you are outside it, your BMI prime (BMI divided by 25), and a colored scale with a marker so you can see where you sit at a glance. A table lists the weight at every category boundary for your height. It is intended for adults aged 20 and over as a quick screening figure; children and teenagers are assessed with age- and sex-specific percentile charts instead.
How it works
BMI = weight in kilograms ÷ (height in meters)². In imperial units the equivalent is 703 × weight in pounds ÷ (height in inches)², which this page evaluates by converting pounds to kilograms (× 0.45359237) and inches to meters (× 0.0254) first, so the two unit systems always agree. Categories follow the WHO cut-offs: below 16 severe thinness, 16–16.9 moderate thinness, 17–18.4 mild thinness, 18.5–24.9 normal, 25–29.9 overweight (pre-obese), 30–34.9 obesity class I, 35–39.9 class II, and 40 or more class III. The healthy weight range is 18.5 × height² to 24.9 × height², and the distance to that range is the difference between your weight and the nearer bound. The scale marker is placed linearly between BMI 15 and 40.
Frequently asked questions
What is a healthy BMI?
For adults the WHO defines 18.5 to 24.9 as the normal range, 25 to 29.9 as overweight, and 30 or more as obese. Some Asian populations carry higher health risks at lower BMI, and several countries (including Japan, China, India, and Singapore) use action points of 23 for overweight and 25 or 27.5 for obesity. Athletes with large muscle mass often read as overweight on BMI while carrying little body fat.
Does BMI work for everyone?
BMI is a population screening tool, not a diagnosis. It cannot tell muscle from fat, does not account for where fat is stored, and reads differently across ages, sexes, and ethnic groups. Very muscular people, older adults who have lost muscle, pregnant women, and children need other measures; waist circumference, waist-to-height ratio, and body fat percentage give a fuller picture. It is not valid for children and teenagers, who are assessed against age-specific percentile charts.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703 and divide by your height in inches squared. A 5 ft 10 in (70 in) person weighing 200 lb has a BMI of 703 × 200 ÷ 4,900 = 28.7. The 703 factor converts the imperial units so that the result matches the metric definition of kilograms per square meter; this page does the conversion for you when you switch the unit toggle.
How much weight do I need to lose to reach a normal BMI?
The calculator shows the weight at which your BMI would be exactly 24.9 for your height and the difference from your current weight. For a 175 cm person, a BMI of 24.9 corresponds to 76.3 kg, so someone weighing 85 kg would need to lose about 8.7 kg. Health guidance generally suggests a gradual rate of about 0.5 to 1 kg (1 to 2 lb) a week, and even a 5 to 10 percent loss brings measurable benefits before the normal range is reached.