Floating roof storage tanks are widely used to store petroleum products with high volatility. This is to prevent product loss and to ensure a safe environment around the storage tanks. The most common sizes of floating roof tanks widely used in the oil industry are small (quarter million barrels), medium (half million barrels) and large (one million barrels) tanks. This article summarises the types of floating roof storage tanks, the derivation of the shell thickness calculation equations due to the stresses which results in from internal pressure of cylindrical geometry and the storage tank shell thickness calculation methods: 1-Foot Method (1-FM) and Variable Design Point Method (VPDM), as recommended by API 650. The article also presents the shell thickness calculations for the small, medium and large storage tanks. This article aids petroleum engineering students, end users, designers in becoming familiar with the storage tank shell thickness calculation guidelines.