[header] How to calculate market share [title] Determine the period you want to examine for each company you are investigating. [step] In order to make sure you are making an apples-to-apples comparison, you must examine sales in a specific time period. You can examine the sales over the length of a quarter, a year, or over several years. 
[title] Calculate the company's total revenue (also called total sales). [step] All publicly-traded companies must release quarterly or annual financial statements.