- Surface area: A full dome consists of 30 rhombus. [If the side of a rhombus is 'l' then its area is l2. Hence the area of dome's surface is 30l2. Maths World says it is 12 5 = 26.83l2. For half a dome the area is 13.415l2. Further if a rhombus is sub-divided into n equal rhombuses of side l each then the surface area of half a dome is 13.415 n2l2.