# Ideal Body Weight Calculator

## Ideal, adjusted, nutritional, BMI, and BSA calculator

### Patient Metrics

 Height in cm Body weight kg lbs Gender Male Female
Press 'Calculate' to view calculation results.

This calculator uses the Devine 1974 ideal body weight equation to describe a patient's "ideal" body weight.1 Although this equation lacks a scientific basis,2 it is extensively used in medicine for a variety of purposes, including drug dosing, mechanical ventilator settings, nutritional requirement assessment, and measurement of renal function.

A patient's ideal body weight (as described by Devine 1974) may be calculated according to the following equation:1

$$\\Ideal\;BW\;(men)\; = 50 + 2.3*(height\;over\;60\;inches) \\Ideal\;BW\;(women)\; = 45.5 + 2.3*(height\;over\;60\;inches)$$

#### Percent ideal weight

Commonly, an "adjustment" for obesity will be calculated in patients who are greater than 20-30% of their ideal body weight. This adjustment varies by indication for adjustment, but is generally an adjustment of 40% for drug dosing or renal function estimations,3 and an adjustment of 25% for nutritional requirement estimation.4

This calculator uses an adjustment factor of 0.4, or 40%, to provide an adjusted body weight in patients who are more than 20% of their ideal body weight. This adjustment uses the following equation:

$$\\AdjustedBW\; = IdealBW + (0.4*(ActualBW - IdealBW))$$

#### Nutritional body weight

This calculator uses an adjustment factor of 0.25, or 25%, to provide a nutritional body weight in patients who are more than 20% of their ideal body weight. Note that some references will use a nutritional body weight on the basis of BMI, rather than percent ideal body weight.5 This adjustment uses the following equation:

$$\\NutritionalBW\; = IdealBW + (0.25*(ActualBW - IdealBW))$$

#### Lean body weight

A more accurate measure of lean body weight may be the LBW2005 equation,6 which unlike the Devine 1974 equation,1 has been derived and validated from actual patient data. Although this equation is less cited in the literature and less commonly used in practice, it may be a useful alternative in the clinical setting for patients who are particularly short (height < 60 inches) or particularly obese. The LBW2005 uses the following equations:

$$\\ LBW2005\;(men) = \frac{9.27*10^3*ActualBW}{6.68*10^3+(216*BMI)} \\ LBW2005\;(women) = \frac{9.27*10^3*ActualBW}{8.78*10^3+(244*BMI)}$$

#### Body mass index (BMI)

BMI is a commonly used measure of obesity outside of the medical setting, but is rarely used within the medical community for clinical decisions. One downfall of the body mass index metric is that it cannot differentiate between lean body weight ("muscle mass") and adipose tissue (fat) because it only takes into account height and weight. The following equation is used to calculate BMI:

$$\\BMI\; = \frac{Weight\;in\;kg}{(Height\;in\;meters)^2}$$

According to the NHLBI,7 BMI can be classified into the following categories:

 Category BMI Underweight Below 18.5 kg/m2 Normal 18.5 to 24.9 kg/m2 Overweight 25.0 to 29.9 kg/m2 Obese - Class I 30.0 to 34.9 kg/m2 Obese - Class II 35.0 to 39.9 kg/m2 Extreme Obesity (Class III) Above 40 kg/m2

#### Body surface area (BSA)

Like BMI, BSA uses both height and weight to describe a patient's body habitus. BMI is commonly used to calculate the dose of chemotherapy agents and to estimate certain cardiac physiologic variables (eg, cardiac output and stroke volume). While there are a number of different BSA equations, the simplest and most commonly used in the hospital setting is a simplified equation by Mosteller 1987.8 Of note, the Mosteller simplified BSA equation has been validated in both adults and children.9

$$\\BSA\; (m^2) = \sqrt{ \frac{Height\;(cm) * Weight\;(kg)}{3600} }$$

1. Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655.
2. Pai MP, Paloucek FP. The origin of the "ideal" body weight equations. Ann Pharmacother. 2000;34(9):1066-9. PMID 10981254.
3. Nicolau DP, Freeman CD, Belliveau PP, et al. Experience with a once-daily aminoglycoside program administered to 2,184 adult patients. Antimicrob Agents Chemother. 1995;39(3):650-5. PMID 7793867.
4. Krenitsky J. Adjusted body weight, pro: evidence to support the use of adjusted body weight in calculating calorie requirements. Nutr Clin Pract. 2005;20(4):468-73. PMID 16207686.
5. Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient: Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (ASPEN). J Parenter Enteral Nutr 2009. 33:277. 10.1177/0148607109335234
6. Janmahasatian S, Duffull SB, Ash S, et al. Quantification of lean bodyweight. Clin Pharmacokinet. 2005;44(10):1051-65. PMID 16176118.
7. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults - The Evidence Report. Bethesda (MD): National Heart, Lung, and Blood Institute; September 1998. Available at http://www.ncbi.nlm.nih.gov/books/NBK2003/.
8. Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098. PMID 3657876.
9. Lam TK, Leung DT. More on simplified calculation of body-surface area. N Engl J Med. 1988;318(17):1130. PMID 3352717.