Market capitalization/capitalisation (aka market cap, mkt cap or capitalized/capitalised value) is a measurement of corporate or economic size equal to the share price times the number of shares outstanding of a public company. As owning stock represents owning the company, including all its assets, capitalization could represent the public opinion of a company's net worth and is a determining factor in stock valuation. Likewise, the capitalization of stock markets or economic regions may be compared to other economic indicators. The total market capitalization of all publicly traded companies in the world was US$51.2 trillion in January 2007 and rose as high as US$57.5 trillion in May 2008 before dropping below US$50 trillion in August 2008.

Valuation

Main: Business valuation

Many companies have a dominant shareholder, which may be a government entity, a family, or another corporation. Many stock market indices such as the (S&P 500, Sensex, FTSE, DAX, Nikkei, Ibovespa, and MSCI) adjust for these by calculating on a "free float" basis, ie the market capitalization they use is the value of the publicly tradable part of the company.

Note that market capitalization is a market estimate of a company's value, based on perceived future prospects, economic and monetary conditions. Stock prices can also be moved by speculation about changes in expectations about profits or about mergers and acquisitions.

It is possible for stock markets to get caught up in an economic bubble, like the steep rise in valuation of technology stocks in the late 1990s followed by the dot-com crash in 2000. Speculation can affect any asset class, such as gold or real estate. In such events, valuations rise disproportionately to what many people would consider the fundamental value of the assets in question. In the case of stocks, this pushes up market capitalization in what might be called an "artificial" manner. Market capitalization is therefore only a rough measure of the true size of a market.

Categorization of companies by capitalization

Traditionally, companies are divided into large-cap, mid-cap, and small-cap. People have rules of thumb to determine category from market capitalization. These need to be adjusted over time due to inflation, population change, and overall market valuation (for example, $1 billion was a large market cap in 1950 but is now not very large), and they may be different for different countries. A common rule of thumb may look like:

• large-cap: over $5 billion
• mid-cap: from $1 billion to $5 billion
• small-cap: under $1 billion

Different numbers are used by different indexes; obviously, no one agrees on the exact cutoffs.