BMI Calculator — Body Mass Index
Body mass index, or BMI, is the quickest way to check whether your weight is in a healthy range for your height. Doctors, insurers and public health agencies across the United States use it as a first screening step, because it needs only two measurements and takes seconds to work out. This free BMI calculator does the maths for you: enter your height in feet and inches and your weight in pounds, or switch to centimetres and kilograms, and you will see your BMI, your weight category and the weight range that counts as healthy for your height. The result is a useful starting point, not a diagnosis. BMI does not measure body fat directly, so it should be read alongside other clues such as your waist size, your activity level and your blood pressure. Use it to track changes over time, to set a realistic weight goal, or to prepare for a conversation with your doctor — and remember that small, steady changes in eating and activity usually matter far more than chasing a single perfect number.
Your BMI Results
Your body mass index
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How to Use
- Choose imperial or metric units at the top of the calculator.
- Enter your height — feet and inches, or centimetres — and your weight in pounds or kilograms.
- Click Calculate to see your BMI, your category and your healthy weight range.
- Compare your result with the categories below, and re-check it every few weeks as your weight changes.
Worked Example
Take a person who is 5 feet 9 inches tall and weighs 170 pounds. First convert the height to inches: 5 × 12 + 9 = 69 inches. Then apply the imperial formula, BMI = 703 × weight in pounds ÷ height in inches squared: 703 × 170 ÷ (69 × 69) = 119,510 ÷ 4,761 = 25.1. That result falls in the 25 to 29.9 band, so it is classed as overweight. The healthy weight range for this height is 125 to 169 pounds, worked out from the 18.5 and 24.9 cut-offs, so reaching 169 pounds would bring this person back into the healthy band. Losing just one or two pounds would already move the BMI close to 24.9, which shows how a modest change can shift the category — but the goal should be lasting healthy habits, not a borderline number.
Understanding BMI Categories
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 and above. Obesity is sometimes split further into class 1 (30 to 34.9), class 2 (35 to 39.9) and class 3 (40 and above), because health risks rise as BMI climbs. These cut-offs come from large population studies linking BMI to the risk of type 2 diabetes, heart disease and other conditions. They are a guide, not a verdict: age, sex, ethnicity, muscle mass and where you carry fat all affect your personal risk. A waist measurement above 40 inches for men or 35 inches for women adds risk even at a healthy BMI, while a fit, muscular person may sit above 25 with very little body fat. If your BMI is outside the healthy range, it is worth discussing with a doctor, who can look at blood pressure, cholesterol, blood sugar and your overall lifestyle before deciding what, if anything, needs to change.
Frequently Asked Questions
What is a healthy BMI?
For most adults, a healthy BMI is 18.5 to 24.9. Below 18.5 is classed as underweight, 25 to 29.9 is overweight, and 30 or above is obesity. These are population-level ranges, so a single number never tells the whole story about your health.
How is BMI calculated?
In imperial units, BMI equals 703 times your weight in pounds divided by your height in inches squared. In metric units, it is your weight in kilograms divided by your height in metres squared. Both formulas give the same result when the units are converted correctly.
Is BMI accurate for athletes?
Not always. BMI cannot tell muscle apart from fat, so a very muscular person can have a high BMI while having little body fat. Athletes and people who lift weights should look at body fat percentage and waist size alongside BMI.
What is a healthy weight for my height?
Multiply 18.5 and 24.9 by your height in inches squared, then divide each result by 703 to get the healthy weight range in pounds. For someone 5 feet 9 inches tall, that range is about 125 to 169 pounds.
Does BMI work for children?
No, adult BMI cut-offs do not apply to children. Children and teenagers are assessed with BMI-for-age percentiles, which compare them with other children of the same age and sex. Ask a pediatrician if you are concerned about a child's weight.