BMI Calculator
Calculate your body mass index from height and weight, then see the result on a visible BMI gauge. The gauge is shown before calculation so users can understand the underweight, healthy weight, overweight, and obesity ranges before entering their own numbers.
How this BMI calculator works
This BMI calculator uses the standard body mass index formula: BMI = weight ÷ height². In metric units, weight is measured in kilograms and height is measured in meters. In US units, the calculator uses the equivalent formula BMI = 703 × pounds ÷ inches². The result is shown in kg/m² because that is the conventional BMI unit.
BMI is widely used because it is fast and easy to compare across adults, but it should be interpreted carefully. The CDC adult BMI category table uses the standard adult ranges of underweight, healthy weight, overweight, and obesity for adults age 20 and older. This calculator follows those same adult ranges for the main category output.
BMI formula for metric and US units
The most common BMI mistake is using centimeters directly in the formula. If your height is 168 cm, the formula needs 1.68 m, not 168. Another common mistake is entering height as “5.10” when you mean 5 feet 10 inches. In US units, 5 feet 10 inches is 70 total inches, not 5.10 feet.
Adult BMI category chart
| BMI | Standard adult category | How to read it |
|---|---|---|
| Less than 18.5 | Underweight | Below the standard healthy adult screening range. |
| 18.5 to 24.9 | Healthy weight | The standard adult healthy-weight range. |
| 25 to 29.9 | Overweight | Above the standard healthy range; context still matters. |
| 30 or higher | Obesity | Usually linked with higher weight-related health risk. |
The NHLBI BMI explanation also presents BMI as a screening method, not a complete diagnosis. That distinction matters because two people with the same BMI can have different body composition and health risk.
Why BMI is useful, but not perfect
BMI is useful because it answers a common first question quickly: “Is this weight generally low, typical, or high for this height?” For many adults, that is enough to start a sensible discussion. But BMI does not separate fat from muscle, does not measure waist size, and does not show blood pressure, blood sugar, cholesterol, or fitness.
The WHO obesity and overweight fact sheet uses BMI as a common population measure, but a personal health decision should look at more than BMI alone. For children and teens, the CDC child and teen BMI category page explains why BMI-for-age percentiles are used instead of adult cutoffs.
Asian BMI interpretation note
Some Asian populations may experience metabolic risk at lower BMI levels than the standard international adult cutoffs. A WHO expert consultation on appropriate BMI for Asian populations discussed additional public-health action points such as 23 and 27.5 kg/m². This calculator keeps the standard adult BMI category as the main result, but the optional Asian note gives extra context for users who need it.
Worked BMI examples
Worked examples help the page rank for informational searches such as “how to calculate BMI,” “BMI formula in kg,” and “BMI formula in pounds and inches,” not just for the calculator keyword itself.
Frequently asked questions
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BMI means body mass index. It compares body weight with height and gives a quick screening number that is commonly used to group adults into underweight, healthy weight, overweight, and obesity categories. BMI is useful because it is simple and easy to compare, but it is not a direct body-fat test. It does not know whether your weight comes from muscle, fat, water, bone structure, or pregnancy-related changes. That is why this calculator shows the result, the visual range, and the healthy weight estimate, while also explaining the limits of BMI.
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In metric units, BMI is calculated as weight in kilograms divided by height in meters squared: BMI = kg ÷ m². In US units, the equivalent formula is BMI = 703 × pounds ÷ inches². The two formulas produce the same BMI when the units are converted properly. The most common manual-calculation mistake is using centimeters directly instead of meters, or treating 5 feet 10 inches as 5.10 instead of converting it to 70 total inches.
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For adults age 20 and older, the standard healthy BMI range is 18.5 to less than 25. A BMI below 18.5 is usually classified as underweight, 25 to less than 30 is classified as overweight, and 30 or higher is classified as obesity. These categories are useful for screening, but they should not be treated as a full medical diagnosis. Waist size, blood pressure, cholesterol, blood sugar, fitness level, age, and medical history can all change how a BMI result should be interpreted.
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The gauge is visible from the start so users can immediately understand the BMI scale before entering values. Before calculation, the needle sits at the healthy-range boundary marker and the output fields show placeholder values. After the Calculate BMI button is pressed, the same gauge updates with the calculated BMI, category, BMI Prime, healthy weight range, and weight difference from the standard healthy range.
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BMI can be misleading for people with high muscle mass. A muscular athlete or manual worker can have a high BMI because muscle adds weight, not because they necessarily have excess body fat. BMI can also miss risk in someone who has a normal BMI but high abdominal fat or low muscle mass. So BMI should be read as a screening number, not a final judgment about body composition or health.
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This calculator can calculate the arithmetic BMI number for anyone, but the adult category labels are designed for adults. Children and teenagers are normally interpreted using BMI-for-age percentiles because healthy ranges change with age and sex during growth. For a child or teenager, use a pediatric BMI percentile approach rather than adult cutoffs.
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BMI Prime compares your BMI with 25, the upper boundary of the standard healthy adult BMI range. The formula is BMI Prime = BMI ÷ 25. A BMI Prime below 1.00 means the BMI is below 25, while a value above 1.00 means it is above the standard overweight threshold. It is a useful quick ratio, but it has the same limitations as BMI itself.
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Some Asian populations may have increased metabolic risk at lower BMI values than the standard adult cutoffs suggest. A WHO expert consultation discussed additional public-health action points such as 23 and 27.5 kg/m² along the BMI continuum for Asian populations. These are not personal diagnoses, but they help explain why a BMI that appears acceptable under standard cutoffs may still deserve attention in some populations when other risk factors are present.
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The calculator estimates the weight range that corresponds to BMI 18.5 to 24.9 for your height. If your current weight is above that range, it estimates how much weight would be needed to reach BMI 24.9. If your current weight is below the range, it estimates how much weight would be needed to reach BMI 18.5. This is only a mathematical estimate; personal goals should also consider body composition, waist size, medical history, and whether a health professional has recommended weight loss, weight gain, or maintenance.
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No. BMI can be a useful starting point, but it should not be your only goal. Many people improve health by improving waist size, strength, fitness, blood pressure, blood sugar, sleep, nutrition quality, and consistency before they reach a particular BMI number. A calculator can help you understand the range, but real health planning should be realistic, sustainable, and based on your wider health context.