### Body Weight

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. Body weight is one way of determining a person's health.

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.[1] 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.[1] Another method of estimating ideal body weight is using the body mass index.

## Average weight around the world

### By region

(millions)
Average weight Overweight population /
total population
Source
Africa 535 60.7 kg (133.8 lb) 28.9% [2]
Asia 2,815 57.7 kg (127.2 lb) 24.2% [2]
Europe 606 70.8 kg (156.1 lb) 55.6% [2]
Latin America and the Caribbean 386 67.9 kg (149.7 lb) 57.9% [2]
Northern America 263 80.7 kg (177.9 lb) 73.9% [2]
Oceania 24 74.1 kg (163.4 lb) 63.3% [2]
World 4,630 62.0 kg (136.7 lb) 34.7% [2]

### By country

Country Average male weight Average female weight Sample population /
age range
Methodology Year Source
Brazil 72.7 kg (160.3 lb) 62.5 kg (137.8 lb) 20–74 Measured 2008–2009 [3]
Canada 80.3 kg (177 lb) Measured [4]
Chile 77.3 kg (170.4 lb) 67.5 kg (148.8 lb) 15+ Measured 2009–2010 [5]
Finland 82.1 kg (181 lb) Measured [4]
Germany 82.4 kg (181.7 lb) 67.5 kg (148.8 lb) 18+ Measured 2005 [6]
South Korea 68.6 kg (151.2 lb) 56.5 kg (124.6 lb) 18+ Measured 2007 [7]
Sweden 81.9 kg (180.6 lb) 66.7 kg (147.0 lb) 16–84 Measured 2003-2004 [8]
UKWales 84.0 kg (185.2 lb) 69.0 kg (152.1 lb) 16+ Measured 2009 [9]
United States 88.3 kg (194.7 lb) 74.7 kg (164.7 lb) 20+ Measured 2003-2006 [10]

#### Global statistics

Researchers at the London School of Hygiene & Tropical Medicine published a study of average weights of adult humans in the journal BMC Public Health and at the United Nations conference Rio+20.[11]

## Stability

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.[12] There are several tape-based systems for estimating children's weight, the most well-known of which is the Broselow tape.[13] 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.[14]

The Leffler formula is used for children 0–10 years of age.[12] In those less than a year old it is

$m = \tfrac\left\{1\right\}\left\{2\right\}a_m + 4$

and for those 1–10 years old it is

$m = 2a_y + 10$

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.[12]

The Theron formula is

$m = e^\left\{0.175571a_y + 2.197099\right\}$

where m and ay are as above.[12]

## 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.