The graph of Charles Law is a graph describing how the volume of a gas changes with respect to its temperature and where the volume is a linear function of the temperature. When the temperature of gas is given in units of Kelvin, the graph intersects the x-axis at 0 K, where the volume is 0. On the other hand, if the temperature is given in units of Celsius, the graph intersects -273 degrees Celsius on the x-axis.
Charles Law states that the volume of a confined gas is directly proportional to its temperature at constant pressure. Because of this property, the equation (volume of gas 1 / temperature of gas 1) = (volume of gas 2 / temperature of gas 2) is often used to determine any one variable if the other variables are known.