Final answer:
The size of the cylinder used for a compressive strength test can vary, but a commonly used size is a 15x30 cylinder.
Step-by-step explanation:
The size of the cylinder used as a standard for a compressive strength test may vary depending on the specific testing standards and requirements. However, one commonly used size for compressive strength tests is a cylinder with a diameter of 15 centimeters (cm) and a height of 30 cm.
This cylinder size is often referred to as a 15x30 cylinder. The cylinder is usually filled with a sample of the material being tested, such as concrete or rock, and subjected to compressive loads to determine its strength.