BMI Calculator
Calculate Body Mass Index (BMI) from height and weight.
About BMI Calculator
BMI Calculator computes body mass index from height and weight and displays an adult-style weight category. Choose metric units for kilograms and centimetres, or imperial units for pounds and inches. It is useful for understanding a BMI figure mentioned in a health record or for learning how the calculation relates weight to height.
BMI is a screening measure, not a diagnosis or a complete assessment of health. The tool asks for only two measurements and cannot distinguish muscle from fat or consider your medical history. Its fixed categories are not a child or teen growth assessment. Use the result as context for a conversation with a health professional, rather than as a target or a treatment recommendation.
How to use BMI Calculator
- Choose units
Select Metric (kg, cm) or Imperial (lb, in) in Units.
- Enter weight
Enter a positive weight in the unit shown beside the field.
- Enter height
Use centimetres in metric mode or total inches in imperial mode. Re-enter measurements if you change units.
- Read both outputs
Review the BMI value and Category. The result updates automatically; read the limitations before interpreting it.
Example: Checking metric inputs
A weight of 70 kg and height of 170 cm give BMI = 70 ÷ 1.7² ≈ 24.2. The tool displays Normal weight for this value; the label alone does not determine an individual’s health.
How it works
In metric mode, height in centimetres is divided by 100 to obtain metres, then BMI is weight in kilograms divided by height in metres squared. In imperial mode, the formula is 703 × weight in pounds divided by height in inches squared. Changing the unit selector changes the interpretation of the entered numbers; it does not convert existing values automatically. Both measurements must be positive before a result is shown.
The category is chosen using the underlying result: below 18.5, below 25, below 30, or 30 and above. The interface labels these Underweight, Normal weight, Overweight and Obese, while the displayed BMI is rounded to one decimal place. A value close to a boundary can round to that boundary while keeping the category of its unrounded value. CDC adult categories are intended for adults aged 20 and older; children and teens need age- and sex-specific interpretation.
When is this useful?
- Understand the calculation behind a recorded adult BMI.
- Check whether the selected height and weight units are correct.
- Prepare a measurement-based question for a health appointment.
Things to know
- This tool does not measure body composition or diagnose health conditions.
- Fixed adult-style labels are not appropriate for assessing children or teens.
- There are no inputs for pregnancy, medical history or muscle mass, and no personalized health recommendations.
Privacy & processing
Height, weight and the selected units are used by a local formula in this browser. These measurements are not sent to a ToolMyth processing API or used to create a health profile.
Further reading
Frequently asked questions
Does changing units convert my measurements?
No. Re-enter your weight and height in the units shown after changing the selector.
Should imperial height be feet or inches?
Total inches. For example, 5 feet 7 inches is 67 inches.
Can children use these category labels?
The tool uses fixed adult-style cutoffs. Children and teens need age- and sex-specific growth assessment, which this calculator does not provide.
Does BMI tell me whether I am healthy?
No. It is one screening measure and does not distinguish fat, muscle and bone. A health professional can interpret it alongside other information.