Common size analysis is a method of comparing either financial statements of different-sized companies or financial statements of one company from different time periods. It achieves these comparisons by measuring some part of a company's financial operations against the totality of the operations. By doing this, common size analysis reduces the raw numbers to percentages that allow for much easier comparison between companies and across time. This method of analysis may be performed on either income statements or balance sheets, but it is only as accurate as the accounting practices used to come up with the numbers.
It is difficult to make financial comparisons between companies, even ones in the same industry, simply because the circumstances between the companies can be so different. By the same token, it is difficult to look at the numbers a company produces in a single year and compare it to what it did, for example, five years ago, as the financial conditions certainly will have changed in that time span. Luckily, common size analysis can be performed, allowing for much more reliable comparisons to be made.
As an example, imagine that a company has total assets measuring $10,000 US Dollars (USD). Out of that total, it has $2,500 USD in cash, $3,500 USD in accounts receivable, and $4,000 USD worth of inventory. To render these different elements for common size analysis, they would all be reduced to a percentage of the total assets. In other words, the cash would be listed at 25 percent, the accounts receivable as 35 percent, and the inventory at 40 percent.
By using common size analysis, comparisons can be more easily made both across time and across the industry. These comparisons are best done using benchmarks. A benchmark could be either another company that is performing well in the industry, or, if a company wishes to measure its performance against its own standards, the benchmark would be a past year in which it performed particularly well. Putting the current numbers up against the benchmark would allow the company to see where its operations might be lacking.
A common size analysis can also be performed on the liabilities that a company has, or it can be performed on its balance sheet as a whole. In this way, elements of a company's operations like debt, shareholder equity, and cost of goods sold can be measured against the financial operations as a whole. The only limit to such analysis is the potential for faulty accounting practices to skew the numbers on which the percentages are based.