Adult BMI: convert height correctly and understand the limits
Check centimetres, metres and the squared-height formula with a worked adult BMI example. Understand why the result is a screening measure.
Method
Body mass index compares body weight with the square of height. The metric formula divides kilograms by metres squared, so its unit is kg/m². The Adult BMI calculator asks for kilograms and centimetres and converts the height internally. Enter 175 in its centimetre field for a height of 1.75 metres; entering 1.75 there would mean 1.75 centimetres and does not represent the intended measurement.
When checking the calculation by hand, divide the centimetre measurement by 100 before squaring. Dividing by 100 after squaring is a different operation and gives the wrong denominator. Convert pounds or feet and inches before using these fields. Keep the measured values consistent and retain extra digits during the calculation; round the final displayed BMI rather than repeatedly rounding intermediate values.
- Entered height175 cm
- Height in metres1.75 m
- Squared height3.0625 m²
- Calculated BMI70 ÷ 3.0625 ≈ 22.9 kg/m²
The calculator takes centimetres; the formula uses metres. Square the height only.
Worked example
For an illustrative adult weighing 70 kg at a height of 175 cm, the height becomes 1.75 m. Squaring it gives 3.0625 m², and dividing 70 by that denominator gives approximately 22.8571 kg/m², or 22.9 to one decimal place. The flow diagram follows these steps. The square applies to the height alone, not to the weight or the entire fraction.
Keeping the same height but changing the example weight to 80 kg gives approximately 26.1224 kg/m², or 26.1. The two bars compare these arithmetic results at a fixed height. They do not recommend changing body weight. A difference between the bars reflects the entered measurements; the calculation does not identify the reason for that difference or measure a change in body fat.
175 cm ÷ 100 = 1.75 m
1.75² = 3.0625 m²
70 ÷ 3.0625 ≈ 22.8571 kg/m²
80 ÷ 3.0625 ≈ 26.1224 kg/m²
- 70 kg example
- 22.857143 kg/m²22.9 kg/m²
- 80 kg example
- 26.122449 kg/m²26.1 kg/m²
Arithmetic examples at 175 cm. These bars are not target weights or a health diagnosis.
Checks and limits
Use this adult interpretation for people aged 20 years and older. Children and teenagers need age-appropriate assessment rather than the same adult interpretation. BMI does not distinguish fat, muscle and bone mass, and it is not a diagnosis or a personal target weight. Consider it with other health information; a health care professional can interpret a result in the individual context.
Related calculators
Source: CDC — About Body Mass Index