Free BMI Calculator
Enter your height and weight to get your body mass index, your weight category, and the healthy weight range for your height.
This free BMI calculator divides your weight by the square of your height (using 703 times pounds divided by inches squared for imperial units, or kilograms divided by meters squared for metric), then maps the result to the standard categories: underweight below 18.5, healthy weight 18.5 to 24.9, overweight 25 to 29.9, and obesity at 30 or above.
BMI is a screening measure, not a diagnosis. It cannot tell muscle from fat, so very muscular people may read high. Talk to a clinician about what your number means for you.
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How BMI math works
Body mass index is weight divided by height squared. In metric units that is kilograms divided by meters squared. In imperial units the formula is 703 times your weight in pounds, divided by your height in inches squared. The 703 is just the unit-conversion constant that makes imperial inputs land on the same scale.
Take a person who weighs 180 pounds and stands 5 feet 10 inches tall. That is 70 inches, and 70 squared is 4,900. Multiply 703 by 180 to get 126,540, then divide by 4,900. The result is 25.8, which lands just inside the overweight band.
The standard adult categories are underweight below 18.5, healthy weight from 18.5 to 24.9, overweight from 25 to 29.9, and obesity at 30 or above. These cutoffs come from population studies linking BMI ranges to health risk, and they apply to adults 20 and older.
You can flip the formula to find your healthy weight range. For 5 feet 10 inches, 18.5 times 4,900 divided by 703 gives about 129 pounds, and 24.9 times 4,900 divided by 703 gives about 174 pounds. So the healthy range at that height is roughly 129 to 174 pounds.
BMI has real limits. It does not distinguish muscle from fat, so athletes with heavy muscle mass often land in overweight territory while staying lean. It also does not account for age, sex, or where fat sits on the body. Use it as a starting point for a conversation with your doctor, not as a final verdict.
BMI calculator questions
What is a healthy BMI?
For adults 20 and older, a BMI from 18.5 to 24.9 is considered the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above falls in the obesity range. Children and teens use BMI percentiles for their age and sex instead of these fixed cutoffs.
How is BMI calculated?
In metric units, divide your weight in kilograms by your height in meters squared. In imperial units, multiply your weight in pounds by 703 and divide by your height in inches squared. Example: 150 pounds at 5 feet 6 inches (66 inches) gives 703 times 150 divided by 4,356, which is 24.2, a healthy BMI.
Is BMI accurate for muscular people?
Not always. Muscle is denser than fat, so athletes and lifters often land in the overweight or even obese bands despite low body fat. For muscular builds, waist measurement, body fat percentage, or a clinician's assessment tells a truer story than BMI alone.
What BMI is considered obese?
A BMI of 30 or higher is classified as obese in adults. It is further divided into class 1 (30 to 34.9), class 2 (35 to 39.9), and class 3 (40 or above). These classes help clinicians gauge risk and choose appropriate treatment paths.