The domes are produced by: the liver on the right, with some contribution from the right kidney and the right suprarenal gland, and the fundus of the stomach and spleen on the left, with contributions from the left kidney and the left suprarenal gland.
Although the height of these domes varies during breathing, a reasonable estimate in normal expiration places the left dome at the fifth intercostal space and the right dome at rib V. This is important to remember when percussing the thorax.