Cost of sales include all expenses that directly contributed to generating revenue.
These expenses vary with the type of business.
Cost of sales, or cost of goods sold (COGS) is defined in a manufacturing firm, such as coca cola as the direct materials (aluminum, water, syrup), direct labor (cost of factory worker) and manufacturing overhead (line manager, utilities, rent, insurance for factory) that went into making only the products that were sold.
Cost of sales for a service like airline might include the direct labor (steward/ess, pilot) and and the direct materials (food, fuel, etc).
