This BMI calculator estimates body mass index from a person’s weight and height. It supports a quick numerical check and explains how to read the result without treating the estimate as a diagnosis.
BMI is a screening index, not a complete description of body composition. The same number can mean different things for children, older adults, athletes, pregnant people, and people with unusual muscle mass or fluid levels.
Body mass index is a ratio of weight to height squared. In metric units, weight is entered in kilograms and height in metres, producing a result expressed as kg/m².
For adults, commonly used screening categories are underweight below 18.5, a reference range from 18.5 to below 25, overweight from 25 to below 30, and obesity at 30 or above. These cutoffs are population-level screening tools, not universal biological boundaries.
BMI = weight (kg) / height (m)²Convert height to metres, square it, and divide weight in kilograms by the squared height.
BMI = 703 × weight (lb) / height (in)²Use pounds and inches consistently. The factor 703 converts the imperial expression to the conventional BMI scale.
The formula is undefined when height is zero. It also becomes unreliable when units are mixed or measurements are entered incorrectly.
A person weighs 70 kg and is 1.75 m tall. What is the BMI?
The BMI is about 22.86. For adults, this falls in the commonly used 18.5–24.9 reference range, but it is not a diagnosis.
A person weighs 154 lb and is 5 ft 8 in tall. What is the BMI?
The BMI is about 23.41. Keep the height unit consistent with the imperial formula.
A person weighs 100 kg and is 1.70 m tall. What is the BMI?
The BMI is about 34.60. Adult category ranges are screening references and should be interpreted with a clinician when health decisions matter.
A person weighs 50 kg and is 1.80 m tall. What is the BMI?
The BMI is about 15.43. A low result can have many causes; it should not be used alone to judge health or nutrition.
A person is 80 kg at 1.75 m and later 75 kg at the same height. What are the two BMI values?
BMI decreases because weight changed while height stayed constant. This describes a numerical change, not the quality or cause of the weight change.
A person weighs 68 kg and is 170 cm tall. What is the BMI after converting height?
The BMI is about 23.53. Converting centimetres to metres before squaring prevents a factor-of-10 error.
A BMI result is a number, not a diagnosis. Adult screening ranges can help identify when a conversation with a health professional may be useful, but they do not establish body-fat percentage or disease risk.
Interpret the result with the measurement date, unit system, age, sex, pregnancy status, muscle mass, and relevant medical context. Do not use one result as the sole reason to start a diet, stop medication, or make another medical decision.
Entering centimetres as metres makes the height wrong after squaring. Convert 170 cm to 1.70 m before calculating.
Mixing pounds with metres or kilograms with inches produces an invalid result. Use matching units.
Rounding height before squaring can change the final number. Keep the measured value and round only at the end.
BMI does not distinguish fat, muscle, bone, or fluid. It is less informative for athletes, people with high muscle mass, older adults, growing children, and some medical conditions.
Adult categories should not be applied to children and adolescents without age- and sex-specific growth references. Pregnancy also requires a different clinical interpretation.
BMI is a screening measure calculated from weight and height. It does not directly measure body fat, fitness, muscle, or overall health.
The metric formula is BMI = weight in kilograms divided by height in metres squared.
Children and teens are generally assessed with age- and sex-specific percentiles, not adult category cutoffs.
Yes. BMI cannot distinguish muscle from fat, so a muscular person may have a high result without the same health profile implied by a population screening range.
Squaring height is part of the standard BMI formula and creates a weight-to-height index.
Convert centimetres to metres before using the metric formula. For example, 170 cm is 1.70 m.
No. It is a screening result. A clinician can consider history, waist size, laboratory findings, age, and other context.
Treat it as an approximate screening signal. Small measurement differences can move a result across a cutoff.
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