Health ToolWHO Clinical Standards

BMI Calculator (Metric & Imperial)

Calculate your Body Mass Index (BMI) instantly. Toggle seamlessly between kilograms/centimeters and pounds/feet, visualize your position on the WHO health spectrum, and determine your ideal target weight.

Personal Parameters

cm
kg
yrs
Your Body Mass Index (BMI)
22.9
Normal healthy weight

WHO Body Mass Classification Scale

22.9
< 18.5 (Under)18.5 – 24.9 (Normal)25 – 29.9 (Over)30+ (Obese)
Healthy Target Weight for Your Height
56.7 kg – 76.3 kg

How BMI Works: The Clinical Formulas

Body Mass Index (BMI), originally conceived by Belgian polymath Adolphe Quetelet in the 19th century, is a standardized international screening tool used by healthcare professionals to assess whether an individual is at an increased risk of weight-related health conditions.

Metric Formula:
BMI = Weight (kg) / [ Height (m) ]²
Imperial Formula:
BMI = 703 × Weight (lbs) / [ Height (in) ]²

Worked Example: Metric & Imperial Calculations

1. Metric Calculation: Height 175 cm (1.75 m), Weight 70 kg

  • Height squared: 1.75 × 1.75 = 3.0625 m²
  • BMI: 70 ÷ 3.0625 = 22.86 (Normal Weight)

2. Imperial Calculation: Height 5 ft 9 in (69 inches), Weight 160 lbs

  • Height in inches squared: 69 × 69 = 4,761 in²
  • BMI: 703 × (160 ÷ 4,761) = 23.62 (Normal Weight)

WHO BMI Categories for Adults

CategoryBMI Range (kg/m²)Health Risk Profile
Underweight< 18.5Nutritional deficiency, weakened immune function
Normal Healthy Weight18.5 – 24.9Lowest statistical risk for chronic metabolic illness
Overweight (Pre-obese)25.0 – 29.9Moderate risk of hypertension, cardiovascular stress
Obese (Class I & II)30.0 – 39.9High risk of Type 2 diabetes, stroke, joint degradation
Severe Obesity (Class III)≥ 40.0Very high clinical risk

Frequently Asked Questions

What is a normal, healthy BMI for adults?

According to the World Health Organization (WHO), a healthy BMI for men and women aged 20 and older is between 18.5 and 24.9. A BMI below 18.5 is categorized as underweight, 25.0 to 29.9 is considered overweight, and 30.0 or higher is classified as obesity.

How do you calculate BMI in metric vs imperial units?

In the metric system, the formula is: BMI = weight (kg) ÷ [height (m)]². In imperial units, the formula is: BMI = 703 × weight (lbs) ÷ [height (inches)]².

Does BMI distinguish between muscle mass and fat?

No. BMI measures total body mass relative to height. It does not differentiate between lean muscle, bone density, water, or adipose body fat. Athletes and strength trainers with substantial muscle may register as "overweight" or "obese" despite having very low body fat percentages. For a more comprehensive body composition assessment, use our US Navy Body Fat Calculator.

Why does BMI differ for children and teens?

Children and adolescents are continually growing, and body fat levels fluctuate between boys and girls. Consequently, BMI for individuals under 20 is plotted against age-and-sex-specific growth percentiles (CDC/WHO growth charts) rather than rigid adult BMI thresholds.

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