A company usually determines the amount of supplies used during a period by:

Supplies used in the period is computed by taking the difference between the balance of the Supplies account and the cost of supplies on hand. The sum of supplies that aren't used as of the balance sheet date must be stated in the asset account Supplies or Supplies on Hand. The supplies that have been used during the accounting period must be stated in the income statement account Supplies Expense. Essentially, supplies are assets until they are used. When they are used, they become an expenditure.