The definition of a kilogram is as far I know,

Kilogram: The mass of a cylinder made of platinum-iridium alloy kept at International Bureau of Weights and Measures is defined as 1 kg.

But it is not possible to go and check that reference all the time. So is there any way to check the accuracy of checking 1kg?

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    $\begingroup$ You can be sure you'll never have exactly 1kg with infinite precision. The thing is: what precisioni is enough for you? Then you'll have to look for an appropiate instrument, and you have to rely on the technical specification and the calibration certificate. $\endgroup$
    – FGSUZ
    May 22, 2018 at 20:30
  • $\begingroup$ I am not asking about much precision. Lets assume It will be ok if I can check if my daily needs bread, flour are exact 1 kg or 999 gm. $\endgroup$ May 22, 2018 at 20:43
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    $\begingroup$ You're missing FGSUZ's point. If you use a kitchen scale to weigh out 1kg of flour, and the readout on the scale says "1000 g", that does not mean that you have exactly 1kg of flour on the scale. Even if your scale was perfectly accurate, it still would only mean that you had somewhere between 999.5 g and 1000.5 g. $\endgroup$ May 22, 2018 at 21:52
  • $\begingroup$ P.S.: amazon.com/dp/B0799J2WJW/ref=sspa_dk_detail_6?th=1 $\endgroup$ May 22, 2018 at 21:56
  • $\begingroup$ Yes that is what i am confused about, how do i know had somewhere between 999.5 g and 1000.5 g. it may be < 999.5 , the weight on amazon, how can i trust that also $\endgroup$ May 23, 2018 at 5:42

1 Answer 1


You measure it on a calibrated scale.

But because local gravity varies by 0.25% around the Earth, you generally have a set of calibrated masses with your scale and (at least on digital scales) a software option to perform a calibration.

These masses are checked against a mass at the maker of the scale, and those masses are checked by a calibration service company, whose masses are checked by some national laboratory, and so on until the original Paris Kg.

This process is a bit annoying, prone to error and ultimately involves carrying lumps of metal to Paris - so there is a plan to redefine the Kg in a way that any laboratory can make their own measurement

  • $\begingroup$ Good answer. This chain of calibrations, from the individual scale via National labs to the international standard, is called "traceability" in metrology (the science of measurements). The plan to redefine the kg will not remove the issue of traceabiltity: while it will enable National labs to reproduce the standard, the individual kitchen scale will probably not use that technology and will still have to be calibrated in the way you describe. $\endgroup$
    – uUnwY
    May 23, 2018 at 8:58

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