Market capitalization, usually shortened to market cap, is the total stock-market value of a company. It is calculated by multiplying the share price by the number of shares outstanding. A company with a share price of 50 and 20 million shares outstanding has a market cap of 1 billion.
Market cap is the most common way to describe how big a listed company is. It tells you the value the market currently puts on the whole business, not the price of one share. It is also the figure used to rank companies, to group them into size bands, and to weight most stock indexes. This guide explains how it is calculated, how to use it, and where it can mislead you.
The formula
Market capitalization = share price × shares outstanding
Shares outstanding is the number of shares the company has issued and that are held by investors, including insiders. It excludes shares the company holds itself in its treasury. The number is published in the company's annual report and in its regulatory filings, and it changes when the company issues new shares, buys back its own shares, or converts other securities into shares.
Many price sites show market cap directly. When you check it yourself, make sure the share count is current, because a company that has issued a large number of new shares recently may have a market cap that is out of date on some sites.
A worked example
Suppose two companies trade at the same share price of 100.
| Company | Share price | Shares outstanding | Market cap |
|---|---|---|---|
| Alpha | 100 | 2 million | 200 million |
| Beta | 100 | 50 million | 5 billion |
The two companies have the same share price, but Beta is 25 times bigger by market value. A share price says nothing about size on its own. This is why a rise of 10 in Alpha's share price and a rise of 10 in Beta's price are very different events for the market as a whole: the first adds 20 million to Alpha's value, and the second adds 500 million to Beta's.
If Beta issues 10 million new shares at 100 to raise money, its share count rises to 60 million and its market cap rises to 6 billion, assuming the price holds. Existing shareholders now own a smaller slice of the company, which is called dilution. Market cap rose because more shares exist, not because the business became more valuable.
Size bands
Investors often group companies by market cap. The bands are a convention, not a rule, and the cut-offs differ between markets and between brokers. A common pattern is:
- Large-cap companies are the biggest, often the names that make up the main index.
- Mid-cap companies sit in the middle of the range.
- Small-cap and micro-cap companies are the smallest, and tend to be less liquid and more volatile.
Each band behaves differently. Large companies usually trade more easily and have more information published about them. Small companies can offer bigger moves in both directions, and they can be harder to sell in a hurry. The cut-off values depend on the market. A company that is large in one country may be small in another, so compare sizes within the same market.
Why market cap matters for an investor
Market cap affects four things that matter to a trader or investor.
Liquidity. Larger companies usually have more shares trading each day, so orders fill more easily and the bid-ask spread is usually narrower. See the guide on the bid-ask spread.
Volatility. Smaller companies often move more on news, because fewer investors own them and each piece of news matters more.
Index weight. Most indexes weight companies by market cap, so large companies move the index more. A small change in a giant company can move the index more than a large change in a small one. The guide on how stock indexes work shows how this works.
Risk of being wrong. The bigger the company, the more its results are watched by analysts, regulators and the press. That does not make it safe, but it does mean less of the information is hidden from you.
Where market cap misleads
Market cap is a snapshot of the market's opinion. It is not the value of the company's assets, and it is not what you would receive if you bought the whole company. A company with a large market cap can still have heavy debt, falling profits or weak cash flow. A company with a small market cap can be sound.
Market cap also ignores debt. Two companies with the same market cap can have very different levels of borrowing. Enterprise value, which adds debt and subtracts cash, is a better measure of what it would cost to buy the whole business, and it is used alongside market cap in serious analysis.
Be careful with share counts that differ between share classes. Some companies have more than one class of shares, with different voting rights or prices. A market cap quoted for one class may not include the other.
Finally, market cap moves with the share price. A market cap of 5 billion on Monday can be 4.5 billion on Friday with no change in the company's business. Check the date of any market cap you use.
Free float and total market cap
Total market cap counts every share, including those held by a government, a parent company or founders who will not sell. Free-float market cap counts only the shares that trade freely. For a company where most shares are locked up, the two figures can differ a lot. Indexes often use free-float figures, because they reflect what a typical investor can actually buy. When you compare companies, check which figure a site is showing.
Using market cap in practice
Start with market cap to put a company in context. It tells you whether you are looking at a giant or a small company, which sets expectations for how it trades. Then check the other measures: the profit, the debt, the trading volume and the share count history. If you are comparing two companies, compare them within the same market and the same size band, because a comparison across very different sizes can mislead.
If you want to own the market rather than pick companies, market cap also tells you how the big index funds will split your money. In a market-cap-weighted index, the largest few companies can make up a large share of the total, which matters for how diversified the fund really is. The guide on index funds vs single stocks explains how to think about that.
Checklist
- Multiply the current price by the current shares outstanding, and check the date.
- Note the size band, and compare only within the same market and band.
- Check the debt, using enterprise value if you have the figures.
- Check whether the company has more than one share class, or has issued or bought back shares recently.
- Use market cap as context, not as a verdict on value.
Key takeaways
Market capitalization is the share price times the shares outstanding. It measures the total market value of a company, which is more useful for sizing a business than its share price. It affects liquidity, volatility and index weight. It ignores debt, changes with the share price, and can be out of date if the share count has changed. Use it to understand what kind of company you are looking at, then test the company on profit, debt and price.
This guide is for general information, not financial advice. See the disclaimer.