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✦ BMI FORMULA & EXAMPLES
BMI Calculation Guide
Learn how to calculate Body Mass Index using weight and height, understand the BMI formula, see worked examples in kg and cm, and use a free online BMI calculator.
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✦ What You’ll Learn
Body Mass Index (BMI) is a simple screening calculation that compares a person's weight with their height. It is commonly used as an initial indicator for adults, but it is not a direct measurement of body fat or a diagnosis of health.
Practical examples
Understand the topic with useful examples and reference values.
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Check your BMI estimate
Use the free InfoJano BMI Calculator and explore your result.
What is the BMI formula?
For weight measured in kilograms and height measured in metres, BMI is calculated by dividing weight by height squared.
BMI = Weight (kg) ÷ [Height (m) × Height (m)]
How to calculate BMI step by step
First convert height from centimetres to metres. Multiply the height in metres by itself. Divide your weight in kilograms by that result. The number you get is your BMI value.
Example: weight 70 kg and height 175 cm. Height in metres = 1.75. BMI = 70 ÷ (1.75 × 1.75) = approximately 22.9.
Calculate BMI online
You can avoid manual arithmetic by entering your weight and height in the InfoJano BMI Calculator. The calculator displays a BMI estimate and, for adults, the commonly used BMI category. Optional age and activity inputs provide additional context for the general guidance shown.
Use consistent units: kilograms for weight and centimetres for height. Measure height without shoes and use a recent weight reading.
What does the BMI number mean?
For adults aged 20 and over, common screening categories are below 18.5 (underweight), 18.5–24.9 (healthy weight range), 25.0–29.9 (overweight) and 30.0 or above (obesity range). These categories are general reference points, not a personal diagnosis.
BMI categories for children and teenagers require age- and sex-specific interpretation. Do not apply adult cut-offs to people under 20.
Limitations of BMI calculations
BMI does not directly measure body fat, muscle mass or fat distribution. It may not fully reflect an individual's age, pregnancy, body composition or medical circumstances. A healthcare professional can interpret BMI alongside other measures and medical history.
If you have concerns about weight or health, seek individual advice from a qualified healthcare professional.
Health information notice: BMI is a screening measure, not a diagnosis. This guide provides general educational information and does not replace advice from a qualified healthcare professional.
? Frequently Asked Questions
How do I calculate BMI manually?
Divide your weight in kilograms by your height in metres multiplied by itself.
What is the BMI formula in kg and cm?
Convert centimetres to metres first, then divide kilograms by metres squared. Equivalently, BMI = weight (kg) ÷ [height (cm) ÷ 100]².
Is a BMI of 22.9 healthy?
For adults, 22.9 is within the commonly used 18.5–24.9 screening range. BMI alone cannot determine overall health.
Can I calculate BMI for a child?
Children and teenagers need BMI-for-age interpretation using age- and sex-specific growth references. Adult categories are not appropriate.
Does BMI measure body fat?
No. BMI uses height and weight and does not directly measure body fat or muscle mass.
BMI calculation keywords
Use this guide to understand the body mass index formula, calculate BMI from kilograms and centimetres, convert pounds and inches, and check a worked BMI example. The BMI formula for adults divides weight in kilograms by height in metres squared. The result is a screening measure, not a diagnosis.
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