The mass of an old bag of cement was one hundredweight (112 pounds, 51 kg). The amount of material that an aircraft could carry into the air is often visualised as the number of bags of cement that it could lift. In the concrete and petroleum industry, however, a bag of cement is defined as 94 lb (43 kg) because it has an apparent volume close to 1 cubic foot (28 litres). When ready-mix concrete is specified, a "bag mix" unit is used as if the batching company mixes 5 literal bags of cement per cubic yard (or cubic metre) when a "5 bag mix" is ordered.