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Body Mass Index (BMI) and Body Surface Area (BSA)

Calculators  Multiple body systems
Body Mass Index and Body Surface Area both utilize weight and height. Body Mass Index can be used to classify a patient as underweight, overweight, and obese. Body Surface Area is able to calculate the body's total surface area.
Body weight


Measured Factor
Body Mass Index, Body Surface Area
Measured Factor Disease
  • Weight category
Measured Factor Detail
Body Mass Index is used to categorize an individual based on weight. Body Surface Area calculates an individual's total body area. These two scores can be used for many different purposes in a variety of settings, including but not limited to dosing and diagnosing.
Body System
Multiple body systems
BMI: weight (kg) / [height (m)]^2 BSA: √[height (cm) x weight (kg)/3600]
Measured Factor Low Impact
  • Underweight
Measured Factor High Impact
  • Overweight patients have a BMI greater than 25.
  • Obese patient have a BMI greater than 30.
  • N/A

Result Interpretation

Ranges Ranges
  • Critical Low: <18.5 kg/meters squared
  • Critical High: >25 kg/meters squared
  • Normal: Results vary according to height and weight; Normal BMI is 18.5-24.9 kg/meters squared
  • Normal Adult Male: N/A
  • Normal Adult Female: N/A
  • Normal Pediatric: N/A
  • Normal Neonate Female: N/A
  • Normal Geriatric Male: N/A
  • Normal Geriatric Female: N/A
Result Low Conditions
  • Cancer
  • tuberculosis
  • hyperthyroidism
  • diabetes
Result High Conditions
  • Hypothyroidism
False Positive
  • N/A
References: 2
Test Limitations
References: 2


Study Validation 1
Firefighters experience a high rate of obesity and heart attacks. The objective of this study was to assess the accuracy of body mass index calculations in determining obese volunteer firefighter. It is thought that firefighters have increased muscle mass. 

90 volunteer firefighters were considered for the study. However, not all participated met the inclusion criteria and body mass index was calculated in 73 male volunteer firefighters. Body mass index calculations were compared to the percent fax. The correlations between body mass index and percent fat was not statistically significant in these subjects. Body mass index calculations should be used cautiously.
References: 3
Study Validation 2
Controversy exists surrounding the accuracy of a body mass index calculation. The body adiposity index (BAI) has been proposed. This included hip circumference and height. The study aimed to compare body mass index, BAI, waist-hip ratio, waist circumference, and hip circumference in their ability to predict fat content.

There was a similar correlation seen between percent body fat and body mass index and percent body fat and BAI. Waist-hip ratio should not be used.
References: 4
Study Validation 3
The aim of the study was to determine the accuracy of self-reported weight and heights in body mass indexes calculations. 

1001 male firefighters in the United States reported their height and weights. Two body mass index calculations were made for each subject. One included the self-reported height and weight. The other included the measured height and weight. A strong correlation was seen between both body mass index calculations.
References: 5
Study Additional 1
The aim of the study was to determine the accuracy of body mass index (BMI) calculations in identifying obese individuals. Bioelectrical impedance was used to determine the amount of body fat. Obesity was defined as a BMI of at least 30, at least 25% body fat in men, at least 30% body fat in women.

The study included 53 males and 88 females. The percent body fat minimum was always met with a BMI of at least 30. 30% of men and 46% of women with a BMI less than 30 were found obese according to their percent body fat. Bioelectrical impedance should be considered in individuals with a BMI less than 30 to confirm no obesity is present.
References: 6
Study Additional 2
The aim of the study was to compare total body fat and body mass index (BMI) calculations in identifying obesity in postmenopausal women. A BMI greater than or equal to 25 is classified as overweight. A BMI greater than or equal to 30 is classified as obese. 

317 women were included in the study. Percent body fat was determined by DXA, a scanner using x-ray waves. Percent body fat and body mass index were able to similarly predict obesity in postmenopausal women.
References: 7
Study Additional 3
In the United Kingdom, it is suggested that all pregnant women should have their body mass indexes calculated. Notes in a hospital were accessed and analyzed retrospectively. The aim of the study was to determine the frequency of these calculations for pregnant women. 

486 notes were included in the study. 90.9% had a body mass index recorded. 26.2% of the sample was overweight. 21.3% of the sample was obese.
References: 8


  1. Gadzik J. "How much should I weigh?"--Quetelet's equation, upper weight limits, and BMI prime. Conn Med. 2006 Feb;70(2):81-8.
  2. N/A
  3. Ode J, Knous J, Schlaff R, Hemenway J, Peterson J, Lowry J. Accuracy of body mass index in volunteer firefighters. Occup Med (Lond). 2014 Apr;64(3):193-7. doi: 10.1093/occmed/kqt143. Epub 2013 Dec 10.
  4. Suchanek P, Kralova Lesna I, Mengerova O, Mrazkova J, Lanska V, Stavek P.Which index best correlates with body fat mass: BAI, BMI, waist or WHR? Neuro Endocrinol Lett. 2012;33 Suppl 2:78-82.
  5. Poston WS, Jitnarin N, Haddock CK, Jahnke SA, Day RS. Accuracy of self-reported weight, height and BMI in US firefighters. Occup Med (Lond). 2014 Jun;64(4):246-54. doi: 10.1093/occmed/kqu040.
  6. Frankenfield DC, Rowe WA, Cooney RN, Smith JS, Becker D. Limits of body mass index to detect obesity and predict body composition. Nutrition. 2001 Jan;17(1):26-30.
  7. Blew RM, Sardinha LB, Milliken LA, Teixeira PJ, Going SB, Ferreira DL, Harris MM, Houtkooper LB, Lohman TG. Assessing the validity of body mass index standards in early postmenopausal women. Obes Res. 2002 Aug;10(8):799-808.
  8. Rees GA, Porter J, Bennett S, Colleypriest O, Ellis L, Stenhouse E. The validity and reliability of weight and height measurements and body mass index calculations in early pregnancy. J Hum Nutr Diet. 2012 Apr;25(2):117-20. doi: 10.1111/j.1365-277X.2011.01207

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