A video decoding method comprising: obtaining, from a bitstream, information about a size of a largest coding unit and information about a minimum size of a coding unit; determining a minimum size of a coding unit with a width and height ratio equal to 1:1 to be same as the minimum size of the coding unit; determining a minimum size of a coding unit with a width and height ratio equal to 1:2 to be a size twice than the minimum size of the coding unit with the width and height ratio equal to 1:1; obtaining, from the bitstream, a value of a difference between the size of the largest coding unit and a maximum size of a coding unit with a width and height ratio equal to 1:4; determining the maximum size of the coding unit with the width and height ratio equal to 1:4 using the information about the size of the largest coding unit and the value of the difference; determining a minimum size of the coding unit with the width and height ratio equal to 1:4 to be a size twice than the minimum size of the coding unit with the width and height ratio equal to 1:2; determining whether it is allowed to split a current coding unit into lower coding units including coding units with a width and height ratio equal to 1:4, based on the maximum size of the coding unit with the width and height ratio equal to 1:4 and the minimum size of the coding unit with the width and height ratio equal to 1:4; when it is determined that it is allowed to split the current coding unit into the lower coding units including coding units with a width and height ratio equal to 1:4, using the minimum size of the coding unit with the width and height ratio equal to 1:4 and the maximum size of the coding unit with the width and height ratio equal to 1:4, splitting the current coding unit into the lower coding units; and decoding the lower coding units. obtaining, from a bitstream, information about a size of a largest coding unit and information about a minimum size of a coding unit; determining a minimum size of a coding unit with a width and height ratio equal to 1:1 to be same as the minimum size of the coding unit; determining a minimum size of a coding unit with a width and height ratio equal to 1:2 to be a size twice than the minimum size of the coding unit with the width and height ratio equal to 1:1; obtaining, from the bitstream, a value of a difference between the size of the largest coding unit and a maximum size of a coding unit with a width and height ratio equal to 1:4; determining the maximum size of the coding unit with the width and height ratio equal to 1:4 using the information about the size of the largest coding unit and the value of the difference; determining a minimum size of the coding unit with the width and height ratio equal to 1:4 to be a size twice than the minimum size of the coding unit with the width and height ratio equal to 1:2; determining whether it is allowed to split a current coding unit into lower coding units including coding units with a width and height ratio equal to 1:4, based on the maximum size of the coding unit with the width and height ratio equal to 1:4 and the minimum size of the coding unit with the width and height ratio equal to 1:4; when it is determined that it is allowed to split the current coding unit into the lower coding units including coding units with a width and height ratio equal to 1:4, using the minimum size of the coding unit with the width and height ratio equal to 1:4 and the maximum size of the coding unit with the width and height ratio equal to 1:4, splitting the current coding unit into the lower coding units; and decoding the lower coding units.