Key takeaways
- Market capitalization is the share price multiplied by the number of shares outstanding: the market's current valuation of the whole company.
- Share price alone says nothing about size: a $50 share can belong to a $250 million company or a $250 billion one.
- FINRA describes typical bands: mega-cap $200 billion or more, large-cap $10–200 billion, mid-cap $2–10 billion, small-cap $250 million–$2 billion, micro-cap under $250 million.
- Larger companies tend to be less volatile than smaller ones, but that is a tendency, not a promise.
- Market cap changes every time the price moves, and many indexes weight their members by it.
How big is a company? On the stock market the standard answer is its market capitalization, or market cap. Investor.gov defines it as the value of a corporation found by multiplying the current market price of one share by the total number of outstanding shares. It is the price the market is currently putting on the whole business, and it is how companies are sorted into the "large-cap", "mid-cap" and "small-cap" labels used throughout investing.
The calculation
Market cap = share price × shares outstanding.
| Company | Share price | Shares outstanding | Market cap |
|---|---|---|---|
| A | $50 | 5 million | $250 million |
| B | $50 | 5 billion | $250 billion |
| C | $400 | 20 million | $8 billion |
The first two rows are FINRA's own example. Both companies trade at $50 a share, yet B is a thousand times larger. FINRA makes the point that newer investors sometimes mistake share price for size, but what matters is the number of shares. Company C has the highest share price and is still far smaller than B.
This is also why a stock split changes nothing about a company's size: the price falls and the share count rises in proportion, leaving market cap where it was.
The size bands
There is no official cut-off, and FINRA notes the delineation can vary, but it describes the usual breakdown:
| Category | Market value |
|---|---|
| Mega-cap | $200 billion or more |
| Large-cap | $10 billion to $200 billion |
| Mid-cap | $2 billion to $10 billion |
| Small-cap | $250 million to $2 billion |
| Micro-cap | Less than $250 million |
Investor.gov's microcap glossary gives a similar boundary, describing companies with market caps under $250 or $300 million as microcap stocks, sometimes called penny stocks, and calls the smallest, under $50 million, "nanocap" stocks. Its stocks guide adds that the very lowest-priced stocks may have little or no earnings and are highly speculative. The SEC adds that pump-and-dump schemes, in which promoters spread false or misleading statements to inflate a price and then sell, typically involve small microcap companies; investment fraud red flags covers how they work.
A size label is not a quality label
"Large-cap" is not a seal of approval and "small-cap" is not a warning. FINRA calls market cap the perceived value of a company, because the stock price is determined by investors, and says it is not necessarily the actual value of the company and all its parts. Some of that perceived value may rest on expectations of future growth that may not pan out, in which case the price, and the market cap, is likely to adjust. Its advice is to look at a number of metrics, not market cap alone. When a fund or article uses a size label, treat it as a description of the holdings, then look at the companies themselves.
What size tells you
FINRA describes market cap as a rough gauge of two things:
- Stage of development. A relatively new public company might have room for growth; FINRA notes that access to investor capital to expand is why many companies go public in the first place.
- Stability. Large-cap companies tend to be less vulnerable to the market's ups and downs than mid-caps, and mid-caps less than small-caps, partly because bigger companies usually have greater financial reserves to absorb a bad year.
FINRA immediately adds that these generalisations are no guarantee for any particular company. A large company can still fall sharply; a small one can thrive.
Market cap moves every day
Because it is built on the share price, market cap changes whenever the price does. It reflects investors' collective expectations, which can swing, not an accountant's measure of what the company owns. A company's book value, its assets minus liabilities, can be very different. Valuation ratios such as the P/E ratio compare the market's price with the company's actual earnings.
Where market cap is used
- Indexes. FINRA notes the S&P 500 is made up of mega- and large-cap stocks and is weighted by market cap, so larger companies account for more of the index, while the Russell 2000 is a small-cap index. What is a stock market index? explains weighting in more detail.
- Funds. FINRA notes that some investment funds also use market cap to group companies by size.
- Diversification. FINRA points out that spreading investments across companies of different sizes is one way to diversify; see diversification explained.
Learn to Trade Stocks Beginner lets you practise reading prices and positions with a virtual balance before any real money is involved. It is one of our education apps; the investing basics hub continues with the valuation ratios.
Good to know
Frequently asked questions
What is market capitalization?
What counts as a large-cap or small-cap company?
Does a higher share price mean a bigger company?
Are small-cap stocks riskier?
Sources
- Market Cap Explained (opens in a new tab)FINRA — accessed
- Market Capitalization (glossary) (opens in a new tab)Investor.gov, U.S. Securities and Exchange Commission — accessed
- Microcap Stock (glossary) (opens in a new tab)Investor.gov, U.S. Securities and Exchange Commission — accessed
- Stocks – FAQs (opens in a new tab)Investor.gov, U.S. Securities and Exchange Commission — accessed
- Updated Investor Alert: Social Media and Investing – Avoiding Fraud (opens in a new tab)Investor.gov, U.S. Securities and Exchange Commission — accessed
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