# Weight

Key: `identity.person.weight`

Person weight in kg, lbs, or other units (e.g., 75kg, 165lbs). Transforms to DOUBLE (kilograms). Decompose extracts value and unit.

Page: <https://meridian.online/docs/projects/finetype/types/identity/person/weight>

Samples: `75 kg`, `165 lbs`, `68.5 kg`, `170 pounds`

## Background

### Origin

Before 2019 the kilogram was tied to a physical object, the International Prototype Kilogram.[[1]](https://www.nist.gov/pml/owm/si-units-mass)

The international yard and pound were agreed by representatives of six nations on 1 July 1959.[[2]](https://en.wikipedia.org/wiki/International_yard_and_pound) The signatories were Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States.[[2]](https://en.wikipedia.org/wiki/International_yard_and_pound) The agreement defined the international pound as 0.45359237 kilograms.[[2]](https://en.wikipedia.org/wiki/International_yard_and_pound) The United States National Bureau of Standards adopted the metric-based units effective 1 July 1959.[[2]](https://en.wikipedia.org/wiki/International_yard_and_pound)

The stone is equal to 14 avoirdupois pounds.[[3]](https://en.wikipedia.org/wiki/Stone_%28unit%29) The stone continues in customary use in the United Kingdom and Ireland for body weight.[[3]](https://en.wikipedia.org/wiki/Stone_%28unit%29)

### Use

NIST's Guide to the SI gives lb as the symbol for the avoirdupois pound and oz for the avoirdupois ounce.[[4]](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9) A number with no unit is the hardest case: decide the unit from the source system's documentation, not from the size of the value, because a heavy adult in kilograms and a light adult in pounds overlap. (Meridian's view)

In the UK and Ireland a body weight may be given in stones and pounds, as in 11 stone 4, meaning 11 stones and 4 pounds.[[3]](https://en.wikipedia.org/wiki/Stone_%28unit%29) A value like 11 stone 4 is two numbers in one field, so split it and convert both parts rather than reading only the leading number. (Meridian's view)

The NHANES 2017-2018 body measures file sets weight to missing for participants with limb amputations.[[5]](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/BMX_J.htm) The same file carries a comment code for weights taken while the participant kept their own clothing on.[[5]](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/BMX_J.htm) Look for companion flags like these before you analyse weights, because a measured weight and a usable weight are not always the same thing. (Meridian's view) Convert everything to kilograms once, keep the original text alongside it, and range-check the result so a mislabelled unit shows up as an outlier. (Meridian's view)

### Where you'll meet it

The CDC's NHANES 2017-2018 body measures file records weight in the variable BMXWT, labelled Weight (kg).[[5]](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/BMX_J.htm) In that file the observed weights run from 3.2 to 242.6 kg.[[5]](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/BMX_J.htm)

## Sources

1. [SI Units - Mass](https://www.nist.gov/pml/owm/si-units-mass) — documentation
2. [International yard and pound](https://en.wikipedia.org/wiki/International_yard_and_pound) — secondary source
3. [Stone (unit) - Wikipedia](https://en.wikipedia.org/wiki/Stone_%28unit%29) — secondary source
4. [NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9) — documentation
5. [Body Measures (BMX\_J)](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/BMX_J.htm) — dataset