What is BMI?
Body mass index (BMI) is a simple number based on your weight and height. Health organizations use it to screen for weight categories that may be linked to health risks. The metric formula is weight in kilograms divided by height in meters squared. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared.
Adult BMI categories
The World Health Organization and the CDC use these ranges for adults: below 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or higher is in the obesity range, which is further split into classes. These categories apply to adults aged 20 and over; children and teens use age- and sex-specific percentiles instead.
Example
A person who is 1.75 m tall and weighs 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which is in the healthy range. Someone 5 feet 6 inches (66 inches) tall weighing 180 lb has a BMI of 180 × 703 ÷ 4,356 ≈ 29.1, in the overweight range. Our BMI calculator does the math for you.
Limitations of BMI
BMI doesn't distinguish between muscle and fat, so athletes with a lot of muscle may be classified as overweight while being very fit. It also doesn't show where fat is stored. Waist circumference, body composition and other health markers such as blood pressure give a fuller picture. Some populations have different risk thresholds, which is why doctors interpret BMI together with other information.
Healthy weight range for your height
To find the weight range that corresponds to a BMI of 18.5 to 24.9, multiply your height in meters squared by 18.5 and by 24.9. For 1.75 m, that gives about 57 to 76 kg. Use our kg to lbs converter if you prefer pounds.
What to do with your result
A BMI outside the healthy range is a reason for a conversation with a healthcare professional, not a diagnosis. Small, sustainable changes in diet, sleep and activity matter more than quick fixes. Our calorie calculator can help you understand your daily energy needs.
Frequently asked questions
What is a healthy BMI for adults?
18.5 to 24.9 according to the WHO and CDC.
How do I calculate BMI in pounds and inches?
Weight (lb) × 703 ÷ height (in)².
Is BMI accurate for athletes?
Not always, because it doesn't distinguish muscle from fat.
Does BMI apply to children?
Children and teens use BMI-for-age percentiles rather than adult categories.