Health & fitness
BMI Calculator
Enter your height and weight in U.S. customary units (feet, inches and pounds) or metric to see your Body Mass Index, the weight category it falls in, and the healthy-weight range for your height. Body Mass Index is the same screening number used on most American doctor's intake forms and by the CDC, so it's a quick way to see roughly where your weight sits before an annual physical. The calculator updates as you type, runs entirely in your browser with nothing sent to a server, and shows the exact formula below. BMI is general information only and is not a diagnosis, so treat your result as a starting point for a conversation with a licensed healthcare provider.
Your measurements
Enter your height and weight
BMI is a screening tool, not a diagnosis. It does not account for muscle mass, body composition, age or pregnancy.
How the BMI calculator works
Body Mass Index (BMI) compares your weight to your height with a single number. It is calculated from your weight in kilograms divided by the square of your height in meters. Imperial inputs (feet, inches and pounds) are converted to metric first, so the result is identical either way.
BMI formula
BMI = weight (kg) ÷ height (m)²where: weight = body weight in kilograms height = height in meters (cm ÷ 100) imperial: kg = lb × 0.45359237, m = (ft × 12 + in) × 0.0254
The healthy-weight range for a given height comes from solving the formula backwards at the category boundaries: weight = BMI × height², using BMI 18.5 (lower) and 24.9 (upper).
BMI categories
- Underweight — below 18.5
- Normal weight — 18.5 to 24.9
- Overweight — 25 to 29.9
- Obese — 30 and above
Notes & assumptions
- Categories follow the World Health Organization classification for adults.
- BMI does not distinguish muscle from fat and is not suitable for children, athletes or pregnancy.
- Calculations are for general information only — consult a healthcare professional before relying on them.
Worked example
Say you're an adult in Ohio who stands 5 ft 9 in tall and weighs 160 lb. First, convert the height to inches: 5 × 12 + 9 = 69 inches, which is 69 × 0.0254 = 1.7526 meters. Next, convert the weight to kilograms: 160 ÷ 2.2046 = 72.57 kg. Now divide weight by height squared: 72.57 ÷ (1.7526 × 1.7526) = 72.57 ÷ 3.0716, which gives a BMI of about 23.6. That lands in the "Normal weight" band (18.5 to 24.9), so no adjustment is needed. To find the healthy-weight range at 5 ft 9 in, multiply each boundary BMI by the height squared: 18.5 × 3.0716 = 56.8 kg (about 125 lb) at the low end and 24.9 × 3.0716 = 76.5 kg (about 169 lb) at the high end. So for this height, a BMI-based healthy weight runs from roughly 125 lb to 169 lb. Change any input above and every number recalculates instantly.
Frequently asked questions
What is a healthy BMI?
For most adults, the standard "normal" or healthy Body Mass Index range is 18.5 to 24.9. Below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 or above as obese. These bands come from the World Health Organization and are also used by the CDC in the United States. They are population-level guides, not a personal verdict — your individual healthy weight depends on factors a calculator can't see, so use the result as general information and talk to your doctor.
What are the limitations of BMI, especially for muscular people?
BMI only uses height and weight, so it cannot tell muscle from fat. A muscular athlete, weightlifter, or football player can have a BMI in the "overweight" or "obese" range while carrying very little body fat, because muscle is denser than fat. BMI also doesn't account for where fat is stored, your age, sex, bone structure, ethnicity, or pregnancy. For those reasons, clinicians often pair BMI with other measures like waist circumference or body-fat testing rather than relying on it alone.
How do I calculate BMI in pounds and inches?
There is a direct imperial formula: BMI = (weight in pounds × 703) ÷ (height in inches)². For example, 160 lb and 69 inches gives (160 × 703) ÷ (69 × 69) = 112,480 ÷ 4,761, which is about 23.6 — the same answer you get by converting to metric. The "703" factor simply bundles the pound-to-kilogram and inch-to-meter conversions into one step so you can stay in U.S. units.
What are the BMI categories?
The standard adult categories are: underweight (below 18.5), normal or healthy weight (18.5 to 24.9), overweight (25.0 to 29.9), and obese (30.0 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). These cutoffs are for adults aged 20 and older; children and teens use separate age- and sex-specific BMI percentile charts.
Is BMI accurate for everyone?
No. BMI is a useful, fast screening tool for populations, but it is less reliable for individuals at the extremes — very muscular people, older adults who have lost muscle, pregnant people, and growing children. It was never meant to diagnose a health condition on its own. Treat your number as general information and ask a licensed healthcare professional to interpret it alongside your overall health, family history, and lab work.