Market Capitalization Explained

Market cap — share price multiplied by shares outstanding — is how the market prices an entire company, and it isn't the same thing as how big that company actually is.

The basic calculation

Market capitalization is simply a company's share price multiplied by its total number of shares outstanding. A company with 500 million shares trading at $40 each has a market cap of $20 billion. It's the market's collective, real-time price tag for owning the entire company, and it changes constantly as the share price moves.

For a deeper look at what shares represent and how they're priced, see AIOVEL's Stocks Explained overview.

Large-cap, mid-cap, and small-cap

Companies are commonly grouped into size categories based on market cap. Large-cap companies, generally in the tens of billions of dollars and up, tend to be established, well-covered by analysts, and relatively more liquid, meaning their shares can typically be bought and sold without moving the price much.

Mid-cap companies sit in between, often still growing but with more of a track record than smaller names. Small-cap companies, generally under a couple billion dollars, tend to carry higher growth potential alongside higher volatility and lower liquidity, since fewer shares trade hands and price swings can be sharper on the same amount of buying or selling pressure.

Market cap isn't the same as company size

It's a common mistake to treat market cap as a stand-in for how big a company actually is. Market cap reflects investor expectations about future profits, not current revenue, assets, or employee count. A fast-growing but unprofitable company can carry a market cap far larger than a mature company with much higher revenue, simply because investors are pricing in expected future growth.

This is also why market cap can move sharply on news that changes expectations — like a shift in growth outlook — even when nothing about the company's current-year revenue or physical assets has changed at all.