BMI Calculator

In metric units, BMI is your weight in kilograms divided by your height in meters squared: BMI = weight ÷ height². In imperial units, BMI is 703 times your weight in pounds divided by your height in inches squared: BMI = 703 × weight ÷ height². A 70 kg adult who is 1.75 m tall has a BMI of 22.86; a 160 lb adult who is 5'10" (70 inches) tall has a BMI of 22.96 - the small difference comes from unit-conversion rounding, not a different formula.

There are four standard BMI categories: underweight is below 18.5, healthy weight is 18.5 to 24.9, overweight is 25 to 29.9, and obese is 30 or above. The obese category is further divided into Class I (30-34.9), Class II (35-39.9), and Class III (40 or above). These ranges are the ones used by the CDC and WHO for adults.

No - BMI is a screening tool, not a diagnostic measurement, and it has known limitations. It does not distinguish between muscle and fat, so athletes and very muscular people are often classified as overweight or obese despite having low body fat. It also does not account for age, gender, or body composition, and is not designed for children, adolescents, or pregnant women, who need different reference tools entirely.

BMI estimates weight status from height and weight alone, while body fat percentage measures the actual proportion of your body that is fat tissue versus lean mass. Two people with an identical BMI can have very different body fat percentages depending on muscle mass, which is exactly why BMI is described as a screening tool rather than a body-composition measurement - body fat percentage is the more precise follow-up question when BMI alone is not enough.

No - BMI only classifies weight status; it does not calculate calorie needs. Daily calorie needs depend on your Basal Metabolic Rate (BMR), the energy your body uses at rest, combined with your activity level. BMI and BMR use some of the same inputs (weight and height) but answer different questions - BMI describes where you are, while BMR and calorie needs describe how much energy your body requires.

BMI tells you which weight category you currently fall into, not a specific target number - your ideal weight is the reverse question: what weight would put you in the healthy range for your height. Ideal weight calculations account for height and typically gender, since healthy weight formulas differ slightly between men and women. If you know your height and want a specific target weight rather than a category, that is a distinct calculation from BMI alone.

Yes - check "Use Imperial Units" and enter your weight in pounds and height in inches instead of kilograms and meters. The calculator uses the standard imperial BMI formula (703 × weight ÷ height²) rather than converting your inputs, so the result is calculated directly in whichever unit system you choose.

No - this calculator, like the standard adult BMI formula, is intended for adults aged 20 and older. Children and teens are assessed using age- and gender-specific BMI percentile charts rather than the fixed adult categories, because healthy body composition changes significantly during growth. BMI is also not a meaningful measure during pregnancy, since weight gain is expected and healthy.

BMI Prime is your BMI divided by 25, the upper edge of the healthy-BMI range, so it is a ratio rather than a kg/m² value. A BMI Prime below 1.0 means your BMI is at or under that healthy-range ceiling; above 1.0 tells you by what fraction you exceed it - for example, a BMI Prime of 1.2 means a BMI 20% above the healthy cutoff. It carries the same information as BMI, just rescaled to make how far above or below the healthy limit you are immediately visible.

Ponderal Index (PI) is weight in kilograms divided by height in meters cubed, rather than squared as in BMI - PI = weight ÷ height³. Because it weights height more heavily, PI is generally considered more reliable than BMI for people at the extremes of height, where BMI can distort results; BMI remains far more widely used in practice because it is simpler and better validated across large populations.

This calculator reports that range directly alongside your BMI: the span of weights, at your exact height, whose BMI falls between 18.5 and 24.9. It is a range rather than one target number because many different weights are equally "healthy" for a given height - a 175 cm adult's healthy-BMI range, for example, spans roughly 57 to 76 kg. If you want a single specific target weight rather than a range, that is a different calculation - see the Ideal Weight Calculator, which uses published height-based formulas instead of the BMI band.