Calculator Body
BMI calculator
BMI is a quick screen that relates your weight to your height. It's useful at population scale and as a rough personal flag — but it can't tell muscle from fat, so read your number with the context below, not as a verdict.
Your BMI
0
By the numbers Context
What a healthy BMI actually means
Body Mass Index was devised in the 1830s by the Belgian mathematician Adolphe Quetelet as a population statistic — never as a diagnosis of an individual. It endures because it is cheap and quick: it needs only height and weight, and it correlates reasonably well with body fat across large groups. For most adults the World Health Organization considers 18.5 to 24.9 the healthy range.
Its weakness is that it is blind to what makes up your weight. Muscle is denser than fat, so athletes and very active people often land in the “overweight” band while being lean and healthy, and BMI can under-flag risk in people who carry little muscle. That is why it is best read alongside other measures — waist size, body fat, and how you actually feel — rather than as the last word.
41.9%
of U.S. adults are in the obesity range (BMI ≥ 30)
CDC/NHANES
18.5–24.9
the healthy BMI range for most adults
WHO
1830s
when the BMI formula was first devised (by Quetelet)
History
Sources: U.S. Centers for Disease Control and Prevention (CDC) / NHANES; World Health Organization.
Frequently asked questions
What is a good BMI for my age?
For adults, the healthy BMI range (18.5–24.9) is the same regardless of age. In older adults, some research suggests a slightly higher BMI can be protective, so clinicians interpret it a little more loosely — but the category cutoffs themselves do not change by age.
How do you calculate BMI correctly?
Divide your weight in kilograms by your height in metres squared (kg ÷ m²). In imperial units, multiply your weight in pounds by 703, then divide by your height in inches squared. This calculator does it for you in either unit.
What is a healthy BMI range?
For most adults: under 18.5 is underweight, 18.5–24.9 is healthy, 25–29.9 is overweight, and 30 or above is the obesity range.
Is BMI accurate?
BMI is an accurate screening tool at the population level and a reasonable first check for individuals, but it cannot distinguish muscle from fat or show where fat is stored. It is best used alongside waist measurement and body-fat percentage, not on its own.
Does BMI account for muscle?
No. BMI uses only height and weight, so it counts muscle and fat the same way. Very muscular people often register as “overweight” by BMI despite being lean, which is one of its best-known limitations.