Body Mass Index (BMI) Information for Adults:
The BMI, BSA, and weight calculator is only accurate in the context of an adult patient > 18 years of age and may not be as accurate in Asian or Pacific Islanders where waist circumference may also be used. For basic information related to children and adolescents please see below.

The following basic World Health Organization (WHO) criteria are used for the basic interpretation of the calculated BMI for general adult population (i.e., non-Asian or non-Pacific Islander).

Underweight: < 18.5 kg/m²
Normal Range: 18.5 - 24.9 kg/m²
Overweight: 25 - 29.9 kg/m²
Obese: ≥ 30 kg/m²

While the calculator does not require this information, the following basic World Health Organization (WHO) criteria are used for the basic interpretation of the calculated BMI for adult people of Asian or Pacific Islander descent.

Underweight: < 18.5 kg/m²
Normal Range: 18.5 - 22.9 kg/m²
Overweight: 23 - 24.9 kg/m²
Obese: ≥ 25 kg/m²

Body Mass Index (BMI) Information for Children & Adolescents:
The WHO and CDC both have criteria for assessing the BMI in people < 19 years of age. In short, while the calculation is still the same as in adults the person's value should be compared to others in their age group to determine what percentile they fall into.  Overweight is defined as a BMI at or above the 85th percentile and lower than the 95th percentile.  Obesity is defined as a BMI at or above the 95th percentile for children of the same age and sex.
For more information and access to a BMI calculator for this group please go to the CDC or WHO.

The Ideal Body Weight (IBW):
The Devine formula was used to calculate the Ideal Body Weight in men: 
IBW (men) = 50 + 2.3 (Height in inches - 60)
The Robinson formula was used to calculate the Ideal Body Weight in women: 
IBW (women) = 45.5 + 2.3 (Height in inches - 60 )

Lean Body Weight (LBW)
This is an estimation of the weight of your body without the weight of fat. Therefore, it represents the weight of your muscles, organs and bones.
The LBW in men = (1.10 x weight in kilogram) - 128([weight in kilogram]² ÷ [100 x height in meters]²)
The LBW in women = (1.07 x weight in kilogram) - 148([weight in kilogram]² ÷ [100 x height in meters]²)

References: 

1.	World Health Organization (WHO). Obesity: Preventing and Managing the Global Epidemic. Geneva: WHO. 1998. WHO
2.	World Health Organization (WHO) Western Pacific Region, International Association for the Study of Obesity, International Obesity Task Force. 2000. WHO
3.	World Health Organization (WHO). The WHO Child Growth Standards. WHO
4.	Centers for Disease Control and Prevention (CDC). Defining Overweight and Obesity. CDC
5.	Centers for Disease Control and Prevention (CDC). Defining Childhood Overweight and Obesity. CDC
6.	Hallynck TH, Soep HH, Thomis JA et al. Should clearance be normalized to body surface or to lean body mass? Br J Clin Pharmacol 1981;11:523-6. PubMed
7.	Verbaecken J, Van de Heyning P, De Backer W et al. Body surface areas in normal-weight, overweight, and obese adults. A comparison study. Metabolism 2006;55:515-24. PubMed
8.	DuBois D, DuBois EF. A formula to estimate the approximate surface are if the height and weight be known. Arch Intern Med 1916;17:863-71.
9.	Gehan EA, George SL. Estimation of the human body surface area from height and weight. Cancer Chemother Rep 1970;54:225-35. PubMed
10.	Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. J Pediatr 1978;93:62-6. PubMed
11.	Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317:1098. PubMed

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