Market capitalization is the simplest way to measure how big a company really is — and it reveals why a $10 stock can be worth far more than a $500 one.
Market capitalization — “market cap” — is the total value of all of a company's shares. The formula is simple:
Market cap = share price × total number of shares
A company with 10 million shares trading at $50 has a market cap of $500 million. This is the figure investors use to judge a company's size, not the share price on its own.
A stock priced at $500 sounds bigger than one at $10 — but if the $500 company has only one million shares ($500M cap) and the $10 company has one billion shares ($10B cap), the “cheap” stock is the giant. Price tells you the cost of one slice; market cap tells you the size of the whole pie.
| Category | Rough range |
|---|---|
| Mega cap | $200 billion and up. |
| Large cap | About $10–200 billion. |
| Mid cap | About $2–10 billion. |
| Small cap | About $300 million–2 billion. |
| Micro cap | Below $300 million. |
Size is a rough proxy for risk and growth. Large caps are usually established, steadier and slower-growing. Small caps can grow faster but swing harder and carry more risk. Market cap is also how stock indexes are built — most weight companies by their cap, as explained in what is a stock market index.
Suppose a company trades at $150 and has 2 billion shares outstanding. Its market cap is $150 × 2,000,000,000 = $300 billion — a large-cap. Notice what this means for price moves: because there are 2 billion shares, every $1 the price moves changes the whole company’s value by $2 billion. Try your own numbers in the market cap calculator.
Major indexes like the S&P 500 are market-cap weighted, meaning the biggest companies move the index the most. In recent years a handful of mega-cap technology names have made up a striking share of the S&P 500’s total value — so when you buy an index fund, you are buying far more of the giants than of the smallest members. That is why two “diversified” funds can behave very differently depending on how concentrated their top holdings are.
Index providers usually use the free-float market cap — only the shares actually available to public investors, excluding large insider or government stakes. A company can have a big total market cap but a smaller float, which affects how much of it ends up in funds and how easily its shares trade.
Not advice: educational content only. For real-world fundamentals see investor.gov.
Put it together with what is a stock and what is an ETF, then trade companies of different sizes in the stock market simulator.
Market capitalization is the total value of a company's shares, found by multiplying the share price by the number of shares outstanding. It measures how big a company is.
Multiply the current share price by the total number of shares outstanding. For example, $50 per share times 10 million shares equals a $500 million market cap.
Because two companies can have the same price but very different share counts. A low-priced stock with billions of shares can be far larger than a high-priced stock with few shares.
Large-cap companies (roughly $10 billion and up) tend to be established and steadier, while small caps (roughly $300 million to $2 billion) can grow faster but are more volatile and risky.