When should "度" be used? When should "量" be used?
度 is measurement for length, height or level  (difference between levels is measured in distance )

量 is measurement for volume (something to do with space available or occupied)

As nouns, they are not interchangeable

量度 (v ) to measure ( length or volume)

量 (v) to measure ( length or volume)

度 (v) to measure ( length)