Find your Body Mass Index, your weight category, and the healthy weight range for your height, using US or metric units.
BMI is a screening measure for adults (age 20 and over). It does not account for muscle mass, bone density, age, or where fat is carried on the body.
Body Mass Index compares your weight with your height. In metric units the formula is weight in kilograms divided by height in meters squared. In US units it is 703 times weight in pounds, divided by height in inches squared. The two formulas give the same answer, and the calculator uses whichever matches the units you pick. When you switch between US and metric, your entries are converted for you.
The result is shown to one decimal place and sorted into the standard adult categories used by the World Health Organization and the CDC. Along with your BMI, the calculator shows your BMI Prime (your BMI divided by 25, where 1.0 is the top of the healthy range), the weight range that would put you between 18.5 and 24.9 at your height, and how far you are from it.
Someone who is 5 feet 9 inches (69 inches) tall and weighs 160 pounds has a BMI of 703 x 160 / 69² = 112,480 / 4,761 = 23.6, which is in the normal weight range. At 69 inches, a BMI between 18.5 and 24.9 corresponds to a weight of about 125.3 to 168.6 pounds, so 160 pounds is inside the range with a BMI Prime of 0.95.
Now take someone who is 5 feet 4 inches tall and weighs 180 pounds. Their BMI is 703 x 180 / 64² = 30.9, which falls in Obesity Class 1. To get to a BMI of 24.9 at that height they would need to weigh about 145.1 pounds, a difference of 34.9 pounds. A third person, 165 cm tall and weighing 50 kg, has a BMI of 50 / 1.65² = 18.4, just under the normal range. Reaching 18.5 would take about 0.4 kg more.
The category is based on the BMI rounded to one decimal, which is how it appears in the result. So a calculated value of 24.96 is shown as 25.0 and counted as overweight, rather than showing 25.0 next to a "normal" label. These cut-offs describe groups of people, not individuals. A BMI of 24.9 is not meaningfully different from a BMI of 25.0.
The healthy range moves with height, because BMI depends on height squared. These are the weights that correspond to a BMI of 18.5 to 24.9 at some common heights, rounded to the nearest pound:
At 6 feet, the thresholds for the higher categories sit at roughly 184 lb for a BMI of 25, 221 lb for 30, 258 lb for 35 and 295 lb for 40.
BMI is popular because it is quick, free and based only on two measurements. It is useful for spotting weight ranges that are linked to higher health risks across large groups of people. It is a screening tool, not a diagnosis, and it has real limits:
Treat your BMI as one data point. If it falls outside the normal range, it is a reason to look at other measures such as waist size, blood pressure, blood sugar and cholesterol, and to talk with a doctor, rather than a verdict on your health. If you and your doctor decide weight change makes sense, small steps count. Health organizations note that losing 5 to 10 percent of body weight can improve blood pressure, blood sugar and other markers. For a 200-pound person, that is 10 to 20 pounds. Use our percentage calculator to work out a percentage of your own weight.
To see how many calories your body uses each day, and what a slow, sustainable deficit or surplus looks like, try the calorie calculator. If you want your exact age in years and months for a health form, the age calculator gives it to you.
If your height or weight is in a unit the form does not use, the unit converter switches between kilograms, pounds, centimeters and inches. BMI is not meant for pregnancy; if you are expecting, the due date calculator shows how far along you are and your key dates.
What is BMI and how is it calculated?
BMI (Body Mass Index) is a number that compares your weight to your height. It is your weight in kilograms divided by your height in meters squared. In US units, multiply your weight in pounds by 703 and divide by your height in inches squared.
What do the BMI categories mean?
For adults, below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is obesity, which is split into Class 1 (30 to 34.9), Class 2 (35 to 39.9) and Class 3 (40 and above). These are population-level screening ranges, not an individual diagnosis.
Is BMI accurate for everyone?
No. BMI does not separate muscle from fat, so very muscular people can show a high BMI with low body fat. It also does not consider age, sex, bone structure or where fat is stored, all of which affect health risk.
What is a healthy BMI range?
For most adults, 18.5 to 24.9 is considered the normal weight range by the WHO and CDC. The calculator converts that range into pounds or kilograms for your height, so you can see the actual weights involved.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the normal range. A value below 1.0 means you are under that limit, and a value above 1.0 means you are over it. For example, a BMI of 22.5 gives a BMI Prime of 0.90, and a BMI of 30 gives 1.20.
Does BMI work for children and teens?
Not with the adult categories. For people under 20, BMI is compared with percentile charts for their age and sex, because body fat changes a lot as children grow. This calculator is intended for adults.
Should I use BMI alone to judge my health?
No. Most health professionals use it together with waist size, blood pressure, blood tests, fitness level and family history. Two people with the same BMI can have very different health profiles.
Is the formula different for metric and US units?
The idea is identical, weight relative to height squared. The US version includes the factor 703 so the numbers line up with the metric scale. Enter the same person in either system and you get the same BMI, apart from tiny rounding differences.