## How much does a kilogram weigh?

CERN:

The Kilogram doesn’t weigh a kilogram any more.

Together with six other units – metre, second, ampere, kelvin, mole, and candela – the kilogram, a unit of mass, is part of the International System of Units (SI) that is used as a basis to express every measurable object or phenomenon in nature in numbers. This unit’s current definition is based on a small platinum and iridium cylinder, known as “le grand K”, that weighs exactly one kilogram. The cylinder was crafted in 1889 and, since then, has been kept safe under three glass bell jars in a high-security vault on the outskirts of Paris.

There is one problem: the current standard kilogram is losing weight. About 50 micrograms, at the latest check. Enough to be different from its once-identical copies stored in laboratories around the world.

These stories have always fascinated me. I bet most people don’t realize the “official” kilogram is an actual physical object.

• rb763

Simple solution. Just tape a 50 microgram coin to the standard….or maybe just tape. 🙂

• Mo

We simply can’t have nice things.

• CuJo YYC

1 kilogram = 1 litre of water at 4ºC at sea level. Not as precise of course, but good enough for cooking and weighing newborn babies. 🙂

• Kip Beatty

FWIW, and I won’t post a link, but if you look on YouTube for the channel “Veritasium”, he’s done some fantastic videos on the actual units of measure including the kilogram (which I don’t think will be an actual physical object any longer). He visits the places where they’re kept, shows them, talks with the keepers, etc. If this stuff interests you, it’s absolutely worth watching.