What is the best measure of capacity of a motor oil?

The best measure of capacity for motor oil is its viscosity, which indicates how easily the oil flows at different temperatures. Viscosity is typically expressed in grades, such as 5W-30, where the "W" stands for winter and the numbers denote the oil's thickness at low and high temperatures. Additionally, the oil's API (American Petroleum Institute) rating can provide insights into its performance and suitability for specific engines. Always refer to your vehicle's owner manual for the recommended oil specifications.