Law of Charles is that the volume of a given mass of a gas at constant pressure is directly proportional to its kelvin (K) temperature.
Temperature is measured by Celsius thermometer and it measures hotness or coldness of body. SI unit of temperature is kelvin (K).
The basic SI unit of Temperature is Kelvin (K). One Kelvin is 1/273.16 of the triple point Temperature of water (273.16K). This scale is called Thermodynamic Temperature Scale.