Market capitalization: how to size up a company

Market capitalization, or market cap, is the total market value of a company's shares. It is the simplest way to answer "how big is this company in the eyes of the market?" A share price on its own cannot tell you that, because two companies with the same price per share can differ enormously in size. Market cap fixes this by multiplying the price by the number of shares.

The formula

Market cap = share price x shares outstanding

Shares outstanding means the shares currently held by investors, including insiders, which excludes shares the company has repurchased and holds in its own treasury. The figure appears on the cover of a company's quarterly and annual reports and changes as the company issues or buys back shares.

If a company has more than one class of shares, the total market cap adds up all classes at their own prices. Data providers differ in how they handle this, which is one reason the same company can show slightly different market caps on different sites. Companies with unequal voting rights are covered in dual-class shares.

Example (illustrative numbers)

Compare two companies:

Company A has a ten times higher share price, but Company B is four times larger by market value. A $20 stock is not "cheaper" than a $200 stock. It is a smaller slice of a bigger company.

Now suppose Company B does a 2-for-1 split. It then has 4 billion shares at $10. The market cap is still $40 billion. Splits change the number of shares and the price per share together, and leave the market cap unchanged (see stock splits and reverse splits).

What causes market cap to change

• Price changes. This is the main driver day to day. If the stock rises 5%, so does the market cap, assuming the share count is stable.
• Issuing shares. Selling new shares, or granting stock to employees, increases the share count, which raises market cap at a given price but dilutes existing owners' stake.
• Buybacks. Repurchasing shares reduces the share count. At an unchanged price, the market cap falls, while each remaining share represents a larger piece of the company.
• Mergers and spin-offs. These can change the share count or split a company's value into two pieces.

Market cap vs enterprise value

Market cap measures only what the stock market says the equity is worth. It ignores how the company is financed. A company with $10 billion of market cap and $5 billion of debt is more heavily burdened than one with no debt.

Enterprise value (EV) adjusts for this. A common version is:

EV = market cap + total debt + preferred stock + minority interests - cash and equivalents

Definitions vary, and some analysts also treat leases or pensions as debt. EV tries to capture the price of buying the entire business, and it is used in multiples like EV/EBIT and EV/EBITDA (see EV to EBITDA and EV to EBIT). Use market cap when comparing the price of the equity, such as in the price-to-earnings ratio, and EV when comparing whole businesses with different amounts of debt.

How to read it

Market cap is mainly a size label. Commonly used labels are large-cap, mid-cap and small-cap, each with its own typical features (see large-cap, mid-cap and small-cap stocks). Cut-offs are conventions, not laws, and index providers set their own.

Rules of thumb: larger companies are usually more heavily traded and more widely analyzed, and smaller companies tend to be more volatile and harder to trade. These are tendencies with many exceptions.

Market cap also drives index weights. In the S&P 500, a company's weight depends on its float-adjusted market cap, so the biggest names have the most influence.

Common mistakes and limits

• Judging size by share price. As the example shows, price alone says nothing about the company's size.
• Treating market cap as what the business is "worth." It is simply the market's current estimate for the equity, and it can be too high or too low. It is not the book value of assets, nor what an acquirer would pay, since buyers usually pay a premium.
• Ignoring debt and cash. Two companies with equal market caps can have very different financial risk. Check the balance sheet.
• Mixing up classes or dates. Market cap uses a specific date's price and share count. Using an outdated share count can mislead, especially after large buybacks or share issuance.
• Forgetting float. Some of the shares may be held by insiders or governments and are not freely traded. Float-adjusted market cap counts only the tradable part.

Where to see it on StocksXray

Stock pages, such as Microsoft's, list a company's peers, which is a quick way to compare a business with others in its industry. Remember that a company's size is only one input; the fundamentals matter more than the label.

Key takeaways

• Market cap = share price x shares outstanding, a measure of the equity's market value.
• Price per share alone does not show size; stock splits change price but not market cap.
• Enterprise value adds debt and subtracts cash to approximate the value of the whole business.
• Size categories are conventions that vary by provider.
• Market cap is a snapshot of market opinion, not a measure of intrinsic worth.

This article is educational and is not investment advice.