SunloopMediaToolsFree Online Tools
4 min read2026-09-21

Understanding Body Mass Index (BMI): Categories & Calculation

Learn the math behind Body Mass Index and how to interpret your health score.

Understanding Body Mass Index (BMI)

Body Mass Index (BMI) is a universal screening metric used to estimate whether body weight falls within a healthy proportion to height.

The BMI Formula

  • Metric System: BMI = (Weight (kg) ÷ [Height (m)]^2)
  • Imperial System: BMI = (Weight (lbs) ÷ [Height (in)]^2) × 703

WHO Weight Classifications

  • Underweight: Below 18.5
  • Normal Weight: 18.5 – 24.9
  • Overweight: 25.0 – 29.9
  • Obesity: 30.0 or greater

What BMI Can and Cannot Tell You

BMI is a screening measure based on height and weight. It does not directly measure body fat or diagnose a health condition, and it may not describe an individual's health equally well across ages, body types, or circumstances. A result is one piece of context; discuss personal health questions with a qualified healthcare professional.

Check your score now using our interactive BMI Calculator.

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