What objects equal 1 kilogram?
For practical purposes, most items in a shop that come in packages saying “1 kg nett weight” weigh 1 kilogram. A more strict definition of 1 kilogram is given by International System of Units. Since 1889, the SI system defines the magnitude of the kilogram to be equal to the mass of the International Prototype Kilogram, often referred to in the professional metrology world as the “IPK”. The IPK is made of a platinum alloy known as “Pt‑10Ir”, which is 90% platinum and 10% iridium (by mass) and is machined into a right-circular cylinder (height = diameter) of 39.17 millimeters to minimize its surface area. The addition of 10% iridium improved upon the all-platinum Kilogram of the Archives by greatly increasing hardness while still retaining platinum’s many virtues: extreme resistance to oxidation, extremely high density, satisfactory electrical and thermal conductivities, and low magnetic susceptibility. The IPK and its six sister copies are stored at the International Bureau of Weights
