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How to use
Body mass index (BMI) relates body weight to height using BMI = weight in kilograms ÷ height in metres squared. Enter weight in kg and height in centimetres: the calculator first converts centimetres to metres, then reports BMI to one decimal place. It also displays common adult screening bands: below 18.5, 18.5 to below 25, 25 to below 30, and 30 or above. These are broad screening categories, not a diagnosis or a direct measurement of body fat. Children's growth, pregnancy, athletic muscle mass and other clinical circumstances call for interpretation beyond this simple adult formula.
- Enter a positive weight in kilograms rather than pounds; convert your measurement before submitting.
- Enter height in centimetres, so 1.75 metres is typed as 175, not 1.75, in the height field.
- Calculate BMI and read both the one-decimal result and the displayed broad adult screening category.
- If a result is close to a category boundary or your situation needs individual care, discuss it with a qualified health professional rather than treating the number as a diagnosis.
How it is calculated
Example
Worked example: a weight of 70 kg and height of 175 cm. First convert 175 cm to 1.75 m, then square the height: 1.75 × 1.75 = 3.0625 m². BMI = 70 ÷ 3.0625 ≈ 22.86, displayed as 22.9. That value falls within the commonly used adult screening range of 18.5 to below 25. A common input mistake is to type 1.75 in a field expecting centimetres; this calculator divides the entered height by 100. The example demonstrates the formula and units, not an assessment of any individual's fitness or health.
Important notes
BMI is an adult population screening indicator, not a direct body-fat measurement or a complete assessment of cardiometabolic risk. Muscle mass, age-related changes in body composition, fluid retention and other factors can make its interpretation misleading. Do not apply adult cut-offs to children or teenagers, who require age- and sex-specific growth assessment; pregnancy and clinical conditions need different evaluation too. The category is computed from the unrounded BMI, while the number displayed is rounded to one decimal, so a boundary value can appear surprising. This is educational information, not personalised medical guidance or a reason to alter treatment.
Worked examples and interpreting results
For an adult weighing 70 kg at 175 cm, BMI is about 22.86. It uses weight divided by height in meters squared and does not directly measure body-fat percentage.
| Case | Calculation | Result |
|---|---|---|
| Height squared in meters | 1.75² | 3.0625 m² |
| BMI | 70 ÷ 3.0625 | 22.857143 kg/m² |
How to check the result
Enter 175 in the centimeter field. Adult categories apply from age 20; children require age- and sex-specific interpretation. BMI is a screening measure, not a standalone diagnosis.
Frequently asked questions
How is BMI calculated in metric units?
Divide kilograms by height in metres squared. At 70 kg and 1.75 m the answer is about 22.9; enter 175 when the field asks for centimetres.
Does a BMI band diagnose a medical condition?
No. Adult BMI categories are screening tools and must be interpreted alongside other health factors; BMI does not measure body fat directly.
Do these categories apply to children or pregnancy?
No. Children and teens need age- and sex-specific growth assessment, while pregnancy and other clinical circumstances require individual interpretation.