It states that According to this volume of given mass of gas is directly propotional to temperature when pressure remains constant.
Mathematically,
V is directly propotional to T
therefore V / T =Constant and V1/T1 = V2/T2
This law can also be definied as volume of a gas increases or decreases by 1/273 of volume of gas at 0 degree Celsius for every 1 degree rise or fall in temperature.