Market capitalisation is the total market value of a company’s equity. It’s calculated by multiplying the current share price by the number of shares outstanding.
The figure updates continuously as the price moves and whenever the share count changes through buybacks, new issues or employee options converting. It’s a simple number that investors use as shorthand for a company’s size in the market.
How market capitalisation is calculated
The core formula is straightforward:
Market capitalisation = share price × shares outstanding
Shares outstanding is the number of ordinary shares held by all shareholders, including those owned by institutions and insiders, but excluding shares the company holds in treasury. Check the latest report or a reliable data provider for the share count, as it can change.
A few mechanics to be aware of:
- Share splits and consolidations. A 2-for-1 split halves the share price and doubles the share count, so market cap is roughly unchanged at the moment of the split. The reverse is true for consolidations.
- Buybacks and new issues. Buybacks reduce the share count, which can lift market cap if the price doesn’t adjust down. New shares issued for funding, acquisitions or employee plans raise the share count, which can dilute existing holders if the market doesn’t see matching value created.
- Multiple classes of shares. If a company has A and B shares with different voting rights, market cap usually includes all classes at their respective prices.
What market cap shows, and what it doesn’t
Market cap is the market’s current estimate of the value of the company’s equity. It’s widely used because it’s quick to compare across companies. A business with a larger market cap is generally considered larger in market terms.
There are limits though:
- It is not enterprise value. Market cap excludes net debt and cash. Enterprise value adjusts for these to approximate the value of the entire business to all capital providers, not just shareholders.
- It is not the takeover price. An acquisition usually involves a premium, transaction costs and changes to the capital structure.
- It does not predict returns. A high or low market cap doesn’t say whether a stock is cheap or expensive. Investors use valuation ratios and fundamental analysis to assess that.
- Liquidity matters. In thinly traded shares, a few prints can move the price a lot, which can make market cap look larger or smaller than it would be in a deeper market.
Where you’ll see market cap used
Size categories. Companies are often grouped by size bands such as large cap, mid cap and small cap. The cut-offs vary by market, index provider and era, so treat them as rough labels, not fixed rules.
Index construction. Most major equity benchmarks weight constituents by market cap, often float-adjusted. That means bigger companies carry more influence on index moves. To see how these benchmarks work more broadly, read our overview of a stock market index.
Screening and allocation. Portfolio builders use market cap to set exposures, compare peers and manage concentration risk. For example, a cap-weighted global fund naturally allocates more to the largest firms.
IPO coverage. When a company lists, the offer price and the post-listing share count imply an initial market cap. This frames early media and analyst discussion. For background on the listing process, see our guide to an IPO.
Crypto context. Data sites rank coins and tokens by market cap too, using token price multiplied by circulating supply. As with equities, definitions of supply can vary by provider.
Float-adjusted and fully diluted variations
Free-float or float-adjusted market cap. Some providers exclude closely held shares that are unlikely to trade soon, such as stakes held by founders, governments or strategic investors. The idea is to reflect the value of the shares actually available to public investors. Most major equity indices use float-adjusted weights.
Fully diluted market cap. This extends the share count to include potential shares from in-the-money options, warrants and convertibles. In practice, you’ll encounter fully diluted figures in deal models and some data services to reflect possible dilution.
Crypto’s “fully diluted valuation” (FDV). In token projects, FDV often means token price multiplied by the maximum supply that could exist if all future emissions or unlocks occur. It can be far above today’s circulating-value figure, especially early in a project’s life.
Definitions vary by provider, so always check what a specific service includes in its market cap number.
A quick example
Imagine Alpha plc trades at £5.00 and has 200 million shares outstanding. Its market cap is £1.0 billion.
- Buyback scenario. If Alpha buys back 10 million shares and the price stays £5.00, shares outstanding fall to 190 million and market cap becomes £950 million. If investors think the buyback improves value, the price might rise, changing the outcome.
- New issue scenario. If Alpha issues 20 million new shares at £5.00 to fund an acquisition seen as value neutral, the share price might still hover around £5.00. Shares outstanding would rise to 220 million and market cap to £1.1 billion.
- Share split. After a 2-for-1 split, Alpha would have 400 million shares at roughly £2.50 each. Market cap would still be about £1.0 billion at the time of the split.
In each case, the basic arithmetic links price and share count, while the market’s view of the company’s prospects drives where the price settles.
Common confusions and pitfalls
- Price versus value. A £10 stock can be bigger than a £100 stock if it has many more shares outstanding. Look at market cap, not just the price per share.
- Book value versus market cap. Book value is the accounting value of equity on the balance sheet. Market cap reflects the market’s forward-looking view, which can be above or below book.
- Dual listings and cross-holdings. Some companies list in multiple markets or own stakes in other listed firms. Data providers may handle these structures differently when tallying shares and weights.
- Illiquid names. In lightly traded stocks, the last trade may not reflect a price that could clear meaningful size, so market cap can mislead if taken too literally.
- Corporate actions lag. After mergers, spin-offs or large option exercises, it can take time for every data source to refresh the share count. If accuracy matters, go back to the company’s latest filings.
Used with a clear view of what’s included in the share count, market capitalisation is a reliable yardstick for comparing company size, building portfolios and understanding how much weight a stock carries in mainstream benchmarks.