BMI Calculator – Body Mass Index & Healthy Weight Tool
Calculate your Body Mass Index (BMI), ideal healthy weight range, and body classification according to World Health Organization (WHO) and CDC standards. Enter your measurements below to get instant results.
How to Calculate BMI
Body Mass Index (BMI) is an anthropometric screening tool used by healthcare organizations, including the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC). It assesses whether an adult is underweight, healthy weight, overweight, or obese based on their height and weight.
1. Metric BMI Formula
BMI = Weight (kg) ÷ [Height (m)]²
Worked Example: If an individual weighs 70 kg and has a height of 1.75 meters (175 cm):
• Height squared = 1.75 × 1.75 = 3.0625 m²
• BMI = 70 ÷ 3.0625 = 22.86 kg/m² (Normal weight).
2. Imperial (US) BMI Formula
BMI = [Weight (lbs) ÷ (Height in inches)²] × 703
Worked Example: If someone weighs 160 lbs and is 5 feet 9 inches tall (69 inches):
• Height squared = 69 × 69 = 4,761 in²
• BMI = (160 ÷ 4,761) × 703 = 23.62 (Normal weight).
Adult BMI Classification Table
Below is the international adult BMI classification established by the World Health Organization (WHO) and adopted by the CDC for adults aged 20 and older:
Understanding the Strengths & Limitations of BMI
While BMI is quick and non-invasive, it should always be considered alongside other body composition markers:
- Body Composition: BMI measures weight relative to height; it does not measure body fat percentage directly or differentiate between muscle mass, bone density, and adipose tissue.
- Fat Distribution: Abdominal visceral fat carries significantly higher health risks than subcutaneous fat on the hips and limbs. Measuring waist circumference provides valuable supplementary insight.
- Ethnic Variations: Studies show that populations of Asian descent often experience metabolic health risks at a lower BMI threshold (e.g. overweight ≥ 23 kg/m²).
Frequently Asked Questions (FAQ)
Does BMI apply to athletes and bodybuilders?
Athletes and weightlifters often have dense, lean muscle tissue, which weighs more than fat by volume. As a result, a muscular athlete may have a BMI above 25 or even 30 (classifying them as overweight or obese on the standard scale) despite maintaining an exceptionally low and healthy body fat percentage (e.g. 8–12%). In these individuals, body fat calipers, DEXA scans, or waist-to-height ratio give a far more accurate assessment.
How is BMI interpreted for children and teenagers?
For children and adolescents aged 2 to 19, the mathematical formula is identical, but the result is interpreted differently using BMI-for-age percentiles. Because body composition changes dramatically during growth and differs between boys and girls, a child’s BMI must be compared against standardized CDC or WHO growth percentiles rather than adult cutoffs. A child between the 5th and 85th percentile is considered normal weight.
What is a healthy BMI for elderly adults (65 and older)?
Epidemiological studies indicate that for seniors aged 65 and older, maintaining a slightly higher BMI (between 23 and 27 kg/m²) may be protective against osteoporosis, involuntary weight loss, and hip fracture during acute illness.
Can BMI alone diagnose health or illness?
No. BMI is strictly a screening metric, not a clinical diagnosis. A comprehensive medical evaluation includes measuring blood pressure, lipid panels (cholesterol, triglycerides), fasting glucose/HbA1c, family history, and physical fitness levels.
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