BMI Calculator: A Practical Guide
Use the BMI Calculator to calculate body mass index from weight in kilograms and height in centimetres. BMI is an adult screening measure, not a diagnosis or a direct measurement of body fat. Interpret it alongside other health information.
How to Use BMI Calculator
- Enter current Weight (kg).
- Enter Height (cm), for example 170 rather than 1.70.
- Select Calculate.
- Read the numerical BMI and discuss health interpretation with a qualified clinician when needed.
BMI Formula and Adult Categories
BMI = weight in kilograms ÷ height in metres squared. The calculator first divides centimetres by 100. A height-unit mistake has a large effect because the height is squared.
The displayed adult bands are below 18.5, 18.5 to below 25, 25 to below 30, and 30 or above. These are screening categories; they do not distinguish muscle from fat or determine an individual treatment plan. Children and teens require age- and sex-specific assessment rather than these adult bands.
Worked Example
At 68 kg and 170 cm, height is 1.70 m. BMI = 68 ÷ (1.70 × 1.70) = approximately 23.53.
Entering 170 as metres or 1.70 in the centimetre field would make the result meaningless. Confirm the units before interpreting any category.
Convert pounds to kilograms: use the Weight Converter.
Convert inches to centimetres: use the Length Converter.
Checks and Common Mistakes
- Do not use an adult category to assess a child.
- Pregnancy, substantial muscle mass and other circumstances can change how useful BMI is.
- Do not change medication or begin a restrictive diet based solely on this number.
- Use measured height and weight where possible instead of rough guesses.
Frequently Asked Questions
Is BMI the same as body-fat percentage?
No. BMI relates weight to height and does not measure body composition. Two people with the same BMI can have different amounts of fat and muscle.
Can I enter pounds or feet?
The visible inputs use kilograms and centimetres. Convert your measurements first and retain enough precision to avoid unnecessary rounding.
Does a category prove that someone is healthy or unhealthy?
No. The category is a screening signal. A clinical assessment may consider medical history, measurements, laboratory findings and other factors.
Related Tools for the Next Step
- Weight Converter: Convert pounds to kilograms.
- Length Converter: Convert inches to centimetres.
- BMR Calculator: Understand a resting-energy estimate.
- Calorie Calculator: Explore estimated maintenance energy needs.
Reference
Further reading: CDC adult BMI categories.