Market share is a company's percentage of sales in a particular industry. Both increases and decreases may affect profits, so managers typically adjust operations and marketing strategies to increase or decrease it as needed. People also look at this figure before they invest in a company, since it can indicate a business's competitiveness. When discussing this topic, it's important to remember that a share market is something different: it's the exchange of companies' stocks.arket share can be calculated either in terms of the money earned from sales or the number of units sold. The basic way of calculating this percentage is just revenue or units sold divided by that of the total market: for instance, if a computer store sold one out of every four computers, it would have a 25% market share. Real-life calculations are a little more difficult though, since the numbers can change drastically based on how a business defines its market. A