BMI Calculator

BMI is weight in kilograms divided by height in meters squared. For US inputs, weight and height are converted before applying the ratio. The CDC adult categories displayed here apply to age 20 and older.

70 kg at 1.75 m gives 70 / 1.75² = 22.86. For adults, the CDC's healthy-weight category is BMI 18.5 to less than 25.

BMI is a screening ratio, not a body-fat measurement or a diagnosis. The same ratio can describe very different muscle and fat distributions.

These adult categories are not appropriate for children and teenagers through age 19, or for assessing pregnancy. Personal health assessment requires more than height and weight.

BMI uses only height and weight, so getting those two measurements right matters more than entering lots of background information. In metric mode, enter height in centimeters and weight in kilograms. A height of 1.75 meters belongs in the box as 175, not 1.75. In imperial mode, enter feet and the remaining inches separately, then weight in pounds. Five feet nine inches is not 5.9 feet, because inches are not decimal tenths of a foot.

For a repeat measurement, use a consistent approach and note the date. Shoes, clothing and different scales can change the inputs without reflecting a meaningful change in your body. Height is squared in the formula, so an incorrect height can affect the result substantially. If the output seems surprising, review the unit selection before interpreting the category. The calculator cannot tell whether a number was copied from a different unit system or measured inaccurately.

At 70 kilograms and 175 centimeters, the ratio is approximately 22.86. Keeping the weight at 70 kilograms but entering a height of 170 centimeters gives approximately 24.22. That difference is produced entirely by the height input; it is not evidence of a change in body composition. This comparison is a useful reminder to use your actual measured height rather than a guessed figure, especially if you are comparing calculations made on different occasions.

The displayed category is selected from the numerical ratio. It does not incorporate age, muscle mass, waist measurements, laboratory results or medical history. The form itself has no age field, so it cannot recognize when an adult classification is being applied to a child. CDC adult categories apply from age 20. For children and teenagers through age 19, assessment uses age- and sex-specific information rather than the adult labels shown by this calculator.

Two people with the same BMI can have different amounts of muscle and body fat. They can also have different health histories and fat distributions. A result inside a named category does not prove that someone is healthy, and a result outside it does not diagnose an illness. BMI is useful as one screening measure precisely because it is simple, but that simplicity also limits what it can tell an individual.

If you discuss the result with a clinician, bring the measurements and any relevant context rather than only the label. A change over time may need to be considered alongside symptoms, medication, pregnancy or changes in activity. The calculator does not evaluate those circumstances and does not recommend a target weight or treatment. It also does not measure body fat. A separate body-composition estimate answers a different question and has its own limitations.

Category boundaries divide a continuous ratio into named ranges. For adults, the CDC healthy-weight category starts at 18.5 and ends below 25. A small input change near a boundary can therefore change the label without representing a sudden biological difference. The ratio used internally can also have more decimal places than the rounded display. If a result is very close to a threshold, pay attention to the underlying inputs rather than treating the rounded number as exact.

Do not use the category as an automatic instruction to gain or lose a particular amount of weight. The calculator has not examined nutritional needs, illness or pregnancy, and adult categories are not a suitable replacement for pediatric assessment. For an important health decision, confirm your measurements and obtain appropriate professional advice. The useful output here is a clearly defined height-to-weight ratio, with a screening category for the population to which those adult thresholds apply.