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BMI Calculator (BMI Range, Healthy Weight & Results)
Calculate Body Mass Index (BMI), WHO weight category, and healthy target weight range.
Body Measurements
Body Mass Index Formula
Transparent mathematical methodology explained in plain English.
Metric: BMI = kg / m² | US: BMI = (703 × lbs) / in² Standard epidemiological formula established by Adolphe Quetelet comparing mass to square of stature.
Variables Explained:
- kg / lbs: Body weight.
- m / in: Height measurement.
Individual 5 ft 10 in (70 in) weighing 165 lbs
US customary calculation.
- Height squared: 70 × 70 = 4,900.
- Weight × 703: 165 × 703 = 115,995.
- BMI = 115,995 / 4,900 = 23.7.
- Category: Normal Weight (18.5 - 24.9 range).
Frequently Asked Questions: BMI Calculator
Click any question below to expand quick answers, formulas, and expert tips.
What is Body Mass Index (BMI) and how is it calculated?
Body Mass Index (BMI) is an internationally recognized screening tool that estimates body fatness based on a person’s height and weight. The metric formula is weight in kilograms divided by height in meters squared (kg/m²), or in US units: (Weight in lbs × 703) ÷ (Height in inches²).
What are the official WHO BMI weight categories?
Underweight: BMI less than 18.5; Normal weight: BMI 18.5 to 24.9; Overweight: BMI 25.0 to 29.9; Class 1 Obesity: BMI 30.0 to 34.9; Class 2 Obesity: BMI 35.0 to 39.9; Class 3 (Severe) Obesity: BMI 40.0 or greater.
What is a healthy BMI range for men and women?
For both adult men and women, a BMI between 18.5 and 24.9 is considered the healthy, optimal weight range associated with the lowest statistical risk of cardiovascular disease and metabolic conditions.
Is BMI accurate for athletes, bodybuilders, and active individuals?
BMI does not differentiate between lean muscle mass and adipose fat tissue. Muscular athletes, bodybuilders, and heavy lifters often register in the overweight or obese BMI ranges despite maintaining healthy, single-digit body fat levels.
What is the BMI formula for US Customary vs. Metric units?
Metric Formula: BMI = Weight (kg) ÷ [Height (m)]². US Customary Formula: BMI = [Weight (lbs) × 703] ÷ [Height (inches)]².
How does age and gender impact BMI interpretation?
For adults 20 and older, standard BMI cutoffs apply uniformly regardless of age or gender. For children and teens aged 2 to 19, BMI is calculated the same way but interpreted using age-and-sex-specific CDC growth percentiles.
What are the health risks of having a high or low BMI?
A BMI over 30 increases risk for type 2 diabetes, hypertension, coronary heart disease, sleep apnea, and osteoarthritis. Conversely, a BMI below 18.5 can indicate malnutrition, osteoporosis, weakened immunity, and anemia.
What is the difference between BMI and Body Fat Percentage?
BMI is an indirect height-to-weight ratio proxy. Body Fat Percentage directly measures the proportion of total body mass composed of adipose tissue vs. lean mass (muscles, bones, organs, and water).