There is no "exact amount". It just takes enough that when spread out under the CPU/GPU that it will fill in the microscopic pores and voids in the metal surfaces. Usually, too much is applied. It takes a very tiny dab for it to spread out under pressure and heat to fill in those voids.
Be careful with the Arctic Silver 5. It is highly conductive (electrically) and can short out circuit boards if applied carelessly. MX-4 is a good alternative and not conductive.