The kilogram has the dubious distinction of being the only SI unit still based on a physical object; specifically, a metal cylinder kept in a vault in France. Plans are well underway to redefine the ...

When we measure the world, we measure it using base units like 'foot,' 'mile,' 'meter,' and 'second.' But who decides how big those units of measurement are? In the United States, those units are ...

After more than a century, the international prototype kilogram – a cylindrical chunk of metal stored in a French vault – doesn't weigh the same as its 40 replicas, distributed worldwide and used to ...

More than a century ago, a small metal cylinder was forged in London and sent to a leafy suburb of Paris. The cylinder was about the size of a salt shaker and made of an alloy of platinum and iridium, ...

One of the most iconic hunks of metal in the world is set to get a demotion. The official metallic cylinder that defines the mass of a kilogram may soon be set aside in favor of a measurement that is ...

Scientists have changed the way the kilogram is defined. Currently, it is defined by the weight of a platinum-based ingot called "Le Grand K" which is locked away in a safe in Paris. On Friday, ...