BMI Calculator

The Body Mass Index (BMI) Calculator can be used to calculate BMI value and corresponding weight status while taking height and weight into consideration. Use the Metric Units tab for the International System of Units (SI) or the Imperial Units tab to convert units into US customary units.

BMI is a measurement of a person's leanness or corpulence based on their height and weight, and is intended to quantify tissue mass. It is widely used as a general indicator of whether a person has a healthy body weight for their height. Specifically, the value obtained from the calculation of BMI is used to categorize whether a person is underweight, normal weight, overweight, or obese depending on what range the value falls between.

These ranges of BMI vary based on factors such as region and age, and are sometimes further divided into subcategories such as severely underweight or very severely obese. Being overweight or underweight can have significant health effects, so while BMI is an imperfect measure of healthy body weight, it is a useful indicator of whether any additional testing or action is required.

BMI Table for Adults (WHO Standards, Age 20+)

This is the World Health Organization's (WHO) recommended body weight classification based on BMI values for adults (men and women age 20 or older):

BMI Categorization for Children and Teens (Age 2-20, CDC)

The Centers for Disease Control and Prevention (CDC) recommends BMI categorization for children and teens using percentile growth curves:

Risks Associated with Being Overweight:

Being overweight increases the risk of a number of serious diseases and health conditions, according to the Centers for Disease Control and Prevention (CDC):

• High blood pressure (hypertension)
• Higher levels of LDL cholesterol ('bad cholesterol') and high triglycerides
• Type II Diabetes & Insulin resistance
• Coronary heart disease and Stroke
• Gallbladder disease & Liver complications
• Osteoarthritis (breakdown of joint cartilage)
• Sleep apnea and respiratory issues
• Certain cancers (endometrial, breast, colon, kidney, liver)
• Increased overall mortality risk compared to those with a healthy BMI

Risks Associated with Being Underweight:

Being underweight has its own associated clinical risks:

• Malnutrition, vitamin deficiencies, and severe anemia
• Osteoporosis (bone fragility and increased fracture risk)
• Decreased immune function and delayed wound healing
• Growth and development issues in children and adolescents
• Possible reproductive issues in women due to hormonal disruption
• Higher mortality risk in surgical procedures

Although BMI is a widely used indicator, it has notable physiological limitations:

• Athletes & Muscular Individuals: Muscle mass is denser than fat tissue. Highly trained athletes or bodybuilders can be classified as 'overweight' or 'obese' despite having low body fat levels.
• Older Adults: Aging leads to muscle loss (sarcopenia). An elderly individual may fall within a 'normal' BMI range while carrying excessive visceral body fat.
• Women vs Men: Women naturally possess higher essential body fat percentages than men for equivalent BMI values.

System Equations:

SI Metric Units: BMI = Mass (kg) / Height² (m)
USC Imperial Units: BMI = 703 × [ Mass (lbs) / Height² (in) ]

BMI Prime:

BMI Prime is the ratio of measured BMI to the normal upper limit of 25 kg/m²:
BMI Prime = BMI / 25
A BMI Prime < 0.74 indicates underweight; 0.74 to 1.0 indicates normal weight; > 1.0 indicates overweight; and > 1.2 indicates obese.

Ponderal Index (PI):

The Ponderal Index uses height cubed rather than squared:
PI = Mass (kg) / Height³ (m)
PI provides greater accuracy for individuals at extreme ends of the height spectrum (very tall or short).