In humans, the right lung is wider, and heavier, but shorter, than the left lung. The left lung is made up of two lobes and the right is made up of three. Each lung is divided into upper and lower lobes. The left lung is a little smaller in size because of the position of the heart.
In other words, the heart gets in the way of the possibility of a larger left lung. In the same way, the position of the liver causes the right hemidiaphragm to be higher than the left. The upper lobe of the right lung contains another triangular subdivision known as the middle lobe