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Depending on their purpose, the capacities of oil tanks can be divided into four types: nominal capacity, storage capacity, operational capacity, and nominal capacity. Taking a 10,000 cubic meter vertical cylindrical oil tank (with a diameter of 30 meters and a wall height of 15 meters) as an example, the following is explained: 1. Nominal capacity: also known as calculated capacity or theoretical capacity. It is the theoretical volume of the oil tank, which is calculated based on the geometric height and diameter of the entire tank. For example: the nominal capacity of this oil tank is: radius × 2 × 3.14 × wall height = 10,600 cubic meters. II. Storage capacity: also known as safety capacity. Due to the presence of devices such as foam generators, high liquid level alarms, or internal floating discs at the top of the oil tank, and for safety reasons, the tank should not be filled to the edge angles of the tank structure; instead, the level should be lowered by about 0.7 meters. For example, the storage capacity of this oil tank = nominal capacity – the volume of the 0.7-meter empty space; that is, 2 × 3.14 × (wall height – 0.7) = 10,100 cubic meters. III. Operating capacity: Also known as operational capacity, it refers to the amount of oil that cannot be extracted from the lower part of the oil outlet pipe (usually at a height of around 0.6 meters) when the tank is in use; this oil remains trapped within the tank. For example, the operating capacity of this oil tank = storage capacity – dead storage capacity; that is, 2 × 3.14 × (wall height – 0.7 – 0.6) = 9,700 cubic meters. IV. Nominal capacity: The nominal capacity is a term used to standardize and serialize storage tanks for convenience; it is an integer value close to the design capacity. For example, we can refer to the oil tank mentioned above as a 10,000-liter oil tank; this figure represents neither the actual storage capacity nor the operational capacity of the tank. It should be noted that the four capacity values of the oil tank mentioned above are based on standard cylindrical geometric dimensions. However, due to actual construction errors in the tank, the space occupied by accessories inside the tank, and an uneven bottom (which is actually conical), there will still be some deviations in the resulting capacity values. Therefore, for oil tanks with high requirements, their storage capacity and operational capacity ultimately need to be determined through volume calibration.