Kilogram (symbol kg) is the basic unit to measure quality in the international system of units, and it is also one of the most commonly used basic units in daily life. One kilogram is defined as Planck constant 6.626070 15× 10? A unit of mass of J.S., almost as heavy as a liter of water. The kilogram is the only basic unit prefixed by the international system of units.

The original definition of kilogram is related to the unit of length.

179 1 year: 4℃ 1 cubic decimeter of pure water. The original device was platinum-iridium alloy, which was preserved in Paris and later called the international kilogram original device.

190 1 the third international metrology conference stipulated that the kilogram is the unit of mass (not weight), which is equal to the original international kilogram. The kilogram is represented by the symbol kg. The kilogram force is a commonly used unit of measurement in engineering technology, which is defined as the gravity of the international kilogram original device at the sea level of latitude 45, and the symbol is kgf.

The word "force" is often omitted in engineering books, which is easily confused with the unit of quality. So in the last century, China stipulated that the use of gravity is also called weight, and the unit is kilogram force.