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 for adults
The table below is the standard WHO adult classification, including the three obesity classes clinicians use. The bands apply to adults aged 20 and over of any sex; children and teens use separate percentile charts.
| Category | BMI range (kg/m²) | Note |
|---|---|---|
| Underweight | Below 18.5 | Can reflect undernutrition or illness; typically worth a conversation about diet and health history |
| Normal weight | 18.5 – 24.9 | The adult reference range associated with the lowest population-level health risk |
| Overweight | 25.0 – 29.9 | A screening flag, not a diagnosis; body composition and waist size add important context |
| Obesity, class 1 | 30.0 – 34.9 | Clinicians typically pair this with blood pressure, blood sugar and cholesterol checks |
| Obesity, class 2 | 35.0 – 39.9 | Higher likelihood of weight-related conditions; usually managed with professional support |
| Obesity, class 3 | 40 and above | Sometimes called severe obesity; specialist care is typically involved |
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: 5 ft 9 in, 175 lb
Take an adult who stands 5 ft 9 in and weighs 175 lb. Height first: 5 × 12 + 9 = 69 inches, and 69 × 0.0254 = 1.7526 meters, so height squared is 1.7526 × 1.7526 = 3.0716 m². Weight next: 175 ÷ 2.2046 = 79.38 kg. Divide weight by height squared: 79.38 ÷ 3.0716 = 25.8, rounded to one decimal the way the tool displays it. The imperial shortcut agrees: (175 × 703) ÷ (69 × 69) = 123,025 ÷ 4,761 ≈ 25.8.
A BMI of 25.8 lands in the overweight band, but only just: the line sits at 25.0, and the healthy range for 5 ft 9 in runs from about 125 to 169 lb (BMI 18.5 and 24.9 times height squared, converted to pounds and rounded to the nearest pound). This person sits roughly 6 lb above the top of that range.
Here is what the number does tell them: weight for height is slightly above the adult reference range, which is a reasonable prompt to watch the trend over time. And what it does not tell them: whether the extra weight is muscle or fat, where it is carried, how fit they are, or anything about blood pressure, blood sugar or cholesterol. Someone who lifts weights three times a week and has a trim waist can hold this exact BMI while being in excellent shape. Treat the result as a starting point for a conversation with a clinician, not a verdict.
Healthy weight range by height
Because the healthy band is defined by BMI 18.5 to 24.9, you can read a weight range straight off any height. The table below solves weight = BMI × height² at both boundaries for a spread of heights, converting to pounds and rounding to the nearest whole pound.
| Height | Healthy weight range |
|---|---|
| 5 ft 0 in | 95 – 127 lb |
| 5 ft 4 in | 108 – 145 lb |
| 5 ft 8 in | 122 – 164 lb |
| 6 ft 0 in | 136 – 184 lb |
| 6 ft 4 in | 152 – 205 lb |
Two things stand out. The band is wide: at 5 ft 8 in it spans about 42 lb, so "healthy weight" describes a range of normal bodies rather than a single number to chase. And it grows quickly with height, because weight scales with height squared: each four-inch step in this table adds roughly 13 to 21 lb to the ends of the band. For a height between two rows, the calculator above gives the exact range.
Where BMI misleads, and what to check instead
Muscular builds. Muscle is denser than fat, so athletes, lifters and people in physically demanding jobs often read as overweight or even obese while carrying little body fat. If you train seriously and your BMI creeps over 25, a body-fat measurement or a simple waist check typically says more about your health than the height-to-weight ratio does.
Older adults. Muscle naturally declines with age, so an older adult can hold a "normal" BMI while carrying relatively little muscle and more fat than the number suggests. Some research also finds that slightly higher BMI values in later life do not carry the same risks as in middle age, which is one reason geriatricians read the number differently for their patients.
Ethnicity. The standard cut-offs were derived largely from European populations. A WHO expert consultation found that many Asian populations face elevated cardiometabolic risk at lower BMI values, and proposed additional action points at 23 (increased risk) and 27.5 (high risk) for screening. Several countries apply lower thresholds in clinical practice, so the same number can be read differently depending on who is interpreting it and for whom.
The useful complement: waist circumference. BMI says nothing about where fat sits, yet abdominal fat is the kind most closely linked to metabolic problems. Common screening thresholds are a waist above about 40 inches for men and about 35 inches for women; some clinicians prefer waist-to-height ratio, with a waist under half your height as the typical guide. A tape measure alongside BMI gives a far better first picture than BMI alone, and a licensed professional can put both numbers in context.
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.
Does BMI use different cut-offs for Asian populations?
The standard 18.5 to 24.9 healthy range is used worldwide, but a WHO expert consultation found that health risks in many Asian populations rise at lower BMI values. It proposed additional action points at 23 (increased risk) and 27.5 (high risk) for public health screening, and some countries, including Singapore and India, apply lower thresholds in clinical practice. If this applies to you, ask your doctor which cut-offs they use.
Should I measure my waist as well as my BMI?
It is a useful complement. Waist circumference captures abdominal fat, which BMI cannot see, and abdominal fat tracks more closely with metabolic risk than overall weight does. Common screening flags are a waist above about 40 inches for men and about 35 inches for women. Measuring both takes a minute and gives a clinician a much better first picture than either number alone.