The kilogram is making history as scientists vote to give it an update for the first time in a century.
Up to now, it has been defined by a golf-ball sized metal cylinder locked in a vault in France, but now the baseline measure is "going electronic".
Paul Hetherington from the National Standards Authority of Ireland said it will not change what you see on your bathroom scales, but it will make measurements more stable for the future.
He said: "Because it's a piece of metal, even though it's handled very carefully and stored very, very carefully, being metal it is subject to contamination. So from that point of view, it's changing by very small amounts, but it is subject to change
"So there has been work ongoing for the last 10 to 20 years in various science laboratories around the world to see can we move away from having a physical artefact so it won't be subject to this change that is ongoing and that is what we voted for."