The term body weight is used colloquially and in the biological and medical sciences to refer to a person's mass or weight. Body weight is measured in kilograms, a measure of mass, throughout the world, although in some countries such as the United States it is measured in pounds, or as in the United Kingdom, stones and pounds. Most hospitals, even in the United States, now use kilograms for calculations, but use kilograms and pounds together for other purposes. Strictly speaking, the body weight is the weight of the person without any items on, but practically body weight is taken with clothes on but often without the shoes and heavy accessories like mobile phones and wallets.
While the terms mass and weight are often used interchangeably in the context of body weight, they actually refer to separate but related concepts in physics. Mass is a measure of an object's inertia and is independent of the effects of gravity, while weight is a measure of the force due to gravity. Thus, if a person were to travel from Earth to the Moon, where there is less gravity, their mass would remain unchanged but their weight would decrease.
Ideal body weight 
Ideal body weight (IBW) was initially introduced by Devine in 1974 to allow estimation of drug clearances in obese patients; researchers have since shown that the metabolism of certain drugs relate more to IBW than total body weight. The term was based on the use of insurance data that demonstrated the relative mortality for males and females according to different height–weight combinations. The most common estimation of IBW is by the Devine formula; other models exist and have been noted to give similar results. Another method of estimating ideal body weight is using the body mass index.
Average weight around the world 
By region 
|Average weight||Overweight population /
|Africa||535||60.7 kg (133.8 lb)||28.9%|||
|Asia||2,815||57.7 kg (127.2 lb)||24.2%|||
|Europe||606||70.8 kg (156.1 lb)||55.6%|||
|Latin America and the Caribbean||386||67.9 kg (149.7 lb)||57.9%|||
|Northern America||263||80.7 kg (177.9 lb)||73.9%|||
|Oceania||24||74.1 kg (163.4 lb)||63.3%|||
|World||4,630||62.0 kg (136.7 lb)||34.7%|||
By country 
|Country||Average male weight||Average female weight||Sample population /
|Brazil||72.7 kg (160.3 lb)||62.5 kg (137.8 lb)||20–74||Measured||2008–2009|||
|Canada||80.3 kg (177 lb)||Measured|||
|Chile||77.3 kg (170.4 lb)||67.5 kg (148.8 lb)||15+||Measured||2009–2010|||
|Finland||82.1 kg (181 lb)||Measured|||
|Germany||82.4 kg (181.7 lb)||67.5 kg (148.8 lb)||18+||Measured||2005|||
|South Korea||68.6 kg (151.2 lb)||56.5 kg (124.6 lb)||18+||Measured||2007|||
|Sweden||81.9 kg (180.6 lb)||66.7 kg (147.0 lb)||16–84||Measured||2003-2004|||
|UK – Wales||84.0 kg (185.2 lb)||69.0 kg (152.1 lb)||16+||Measured||2009|||
|United States||88.3 kg (194.7 lb)||74.7 kg (164.7 lb)||20+||Measured||2003-2006|||
|This section does not cite any references or sources. (March 2011)|
The stability of body weight depends on the energy intake and expenditure. When energy intake exceeds output, the excess energy is stored in the body as carbohydrates, proteins or fats and this causes a gain in body weight. The converse is also true. When energy expenditure exceeds energy intake, body weight decreases.
Estimation in children 
A number of ways to estimate weight in children have been developed for circumstances (such as emergencies) when actual weight cannot be measured. The most commonly used methods include guesses of the child's weight by parents or healthcare providers, weight-estimation formulas based on the child's age and tape-based systems of weight estimation. Some of the many formulas that have been used include the APLS formula, the Leffler formula, and Theron formula. There are several tape-based systems for estimating children's weight, the most well-known of which is the Broselow tape. The Broselow tape is based on length with weight read from the appropriate color area. Newer systems, such as the PAWPER tape, make use of a simple two-step process to estimate weight: the length-based weight estimation is modified according to the child's body habitus to increase the accuracy of the final weight prediction.
The Leffler formula is used for children 0–10 years of age. In those less than a year old it is
and for those 1–10 years old it is
where m is the number of kilograms the child weighs and am and ay respectively are the number of months or years old the child is.
The Theron formula is
where m and ay are as above.
Sports usage 
Participants in sports such as boxing, mixed martial arts, wrestling, rowing, judo, and weight-lifting are classified according to their body weight, measured in units of mass such as pounds or kilograms. See, e.g., wrestling weight classes, boxing weight classes, judo at the 2004 Summer Olympics, boxing at the 2004 Summer Olympics.
See also 
- Bergmann's Rule
- Birth weight
- Body mass index
- Body volume index
- Hesse's Rule
- Human height
- List of the heaviest people
- Weight loss and weight gain
- Weight phobia
- Pai, Manjunath P; Paloucek, Frank P (31 August 2000). "The Origin of the “Ideal” Body Weight Equations". The Annals of Pharmacotherapy 34: 1066–1069. doi:10.1345/aph.19381. PMID 10981254.
- Walpole, Sarah C et al (18 June 2012). The weight of nations: an estimation of adult human biomass. BMC Public Health 2012, 12:439. doi:10.1186/1471-2458-12-439. Retrieved 12 July 2012.
- Do G1, em São Paulo (2010-08-27). "G1 - Metade dos adultos brasileiros está acima do peso, segundo IBGE - notícias em Brasil". G1.globo.com. Retrieved 2012-07-13.
- "Average Male Weight". Retrieved 2013-04-16.
- Encuesta Nacional de Salud 2009–2010 (p. 81)
- "Average Male Weight". Retrieved 2013-04-16.
- © wissenmedia in der inmediaONE] GmbH, Gütersloh/München. "Bauer sucht Frau aus dem Lexikon" (in (German)). wissen.de. Retrieved 2012-07-13.
- "The Chosun Ilbo (English Edition): Daily News from Korea - Average Korean Now Overweight". English.chosun.com. 2009-07-27. Retrieved 2012-07-13.
- "6 kilo mer man och 4 kilo mer kvinna" (in Swedish). Retrieved 2013-04-16.
- "The Welsh Health Survey 2009, p. 58". Wales.gov.uk. 2010-09-15. Retrieved 2011-01-22.
- "Anthropometric Reference Data for Children and Adults: United States, 2003–2006" (PDF). Retrieved 2012-10-25.
- So TY, Farrington E, Absher RK (June 2009). "Evaluation of the accuracy of different methods used to estimate weights in the pediatric population". Pediatrics 123 (6): e1045–51. doi:10.1542/peds.2008-1968. PMID 19482737.
- Lubitz, Deborah (1988). Ann Emerg Med 17 (6). PMID 3377285.
- Wells, Mike (2011). Sanguine 1 (2) http://www.ecssa.org.za/images/sanguine/2011/2011-2-4.pdf
|url=missing title (help). Retrieved 4 February 2012.