BMI Calculator

Calculate your Body Mass Index — a screening measure based on height and weight.

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BMI Calculator

Body Mass Index

Body Mass Index, or BMI, is a simple screening calculation based on height and weight. It is commonly used to group adult body weight into broad categories.

How do you calculate BMI?

Metric: BMI = weight in kilograms ÷ height in metres².

Imperial: BMI = (weight in pounds × 703) ÷ height in inches².

Adult BMI categories

Coach Plum uses the standard adult category boundaries: Underweight below 18.5, Normal from 18.5 to below 25, Overweight from 25 to below 30, and Obese at 30 or above.

What are the limitations of BMI?

BMI does not distinguish fat mass from muscle mass and does not describe where body fat is stored. A muscular person can therefore have a high BMI without having the same body composition as another person with the same BMI.

BMI is best treated as one screening measure rather than a complete description of health or fitness. If you provide body-fat percentage, Coach Plum also shows estimated lean mass, fat mass, FFMI and FMI to add more context.

When does Coach Plum show health guidance?

If BMI is below 18.5, the results page shows an NHS-based Health Guidance notice. The calculation remains visible; the notice adds context rather than blocking the result.