BMI Calculator: Body Mass Index

What is BMI and how is it calculated?

Body mass index, or BMI, puts body weight in relation to height. It is a screening index, not a body-fat measurement or a complete assessment of health. It is also known as a height-to-weight index.

BMI = weight (kg) ÷ height squared (m²). At 70 kg and 175 cm: 70 ÷ 1.75² = 22.9 kg/m².

Measure height without shoes and compare weight under similar conditions. Choose kilograms and centimetres or pounds and inches; changing units converts the figures already entered. For example, 5 ft 9 in is 69 inches. This calculator is for adults aged 18 and over and does not assign adult categories to children.

Understanding adult BMI categories

Categories use the unrounded calculation, while the main result displays one decimal place. A number very close to a boundary may therefore appear rounded to that boundary. These categories help start a discussion; they should be considered alongside weight history, waist size and other findings. The CDC’s explanation of BMI describes this screening role.

Is the displayed weight range my ideal weight?

The tool applies BMI values of 18.5 and 24.9 to your height. At 175 cm, that gives about 56.7–76.3 kg. It does not mean you should aim for the midpoint. Your usual weight, muscle mass and health circumstances can change what is appropriate. The ideal weight range calculator explains the difference between a population reference and a personal goal.

What does waist-to-height ratio add?

An optional waist measurement gives a second index: waist divided by height, using the same unit. An 85 cm waist at a height of 175 cm gives 0.49. Measure midway between the lowest rib and the top of the hip bone after breathing out normally, and use the same site each time.

Waist-to-height ratio can add context about central fat distribution; it does not directly measure visceral fat. NICE guidance discusses combining this measure with BMI in suitable adults and considering ethnicity. A single adjustment should not be applied automatically to everyone from a particular country.

BMI in women, men, athletes and older adults

The basic adult equation is the same for women and men, so sex is not needed for this calculation. Two people with the same BMI can have different amounts of muscle and fat. For someone who strength trains, a higher BMI may reflect muscle mass. A tape-based body-fat estimate offers another perspective, with its own measurement limitations.

In older adults, muscle loss and unintentional weight change deserve attention alongside BMI. This tool does not assign a separate ideal range to everyone over 65. Pregnancy changes the interpretation of weight, while children and teenagers need age-appropriate growth assessment.

Using the result sensibly

Check the measurements first and avoid treating small daily changes as lasting progress. If you are exploring weight management, the daily calorie calculator answers a different question: estimated energy needs. A BMI result alone does not prescribe calories, diagnose a condition or predict a weight-loss timeline.