Market Cap (Market Capitalization)
Current share price × shares outstanding — what the whole company would cost at today's price (the company's size).
In plain terms
Market cap is what it would cost to buy up every single share at today's price. In other words, "the value the market puts on the whole company" — the company's "size."
Even at a $500 share price, with only 1M shares the market cap is $500M; even at a $50 price, with 1B shares it is $50B. The real size is market cap, not the per-share price.
What it tells you
Market cap is the basis for sorting companies into large-, mid-, and small-cap. By size, price volatility, ease of buying and selling, and the indices a stock is included in all change, making it the starting point that separates investment character.
Other valuation metrics like PSR (price-to-sales) and enterprise value (EV) are all computed on market cap.
Formula
market cap = current share price × shares outstanding
What high or low means
A large market cap means the market put a large value on it — it does not by itself mean "expensive or cheap." Expensiveness is seen relative to profit or assets (PER, PBR).
Within the same industry, a larger market cap usually tends to be more mature and stable, while a smaller one tends to carry more room to grow along with more volatility.
Market cap is not the true price of buying the whole company. If you acquire it you also take on its debt, while you get the company's cash. So what is closer to the real acquisition price is enterprise value (EV = market cap + net debt). For a heavily indebted company, EV is far larger than market cap.
Shares outstanding include stock not yet floated to the market (held by large holders and insiders). So it can differ from the size reckoned on only the shares actually traded in the market.
If stock options and convertibles later turn into shares, the share count rises, so the very share count underlying the market-cap calculation can change.
Market cap matters because the flagship US index, the S&P 500, holds stocks in proportion to market cap. So a few giant companies sway the whole index — in 2024, just the top seven firms like Apple and Nvidia made up about a third of the S&P 500.
This creates situations where "the index rose but my stock fell." The underperformance of the many other stocks is hidden behind an index pulled up by a few giants. Note that a company's size should be seen by market cap, not the per-share price — just as a stock split lowers the per-share price while market cap stays the same, market cap is not a mere "size number" but the weight that moves the market.
Metrics to read alongside
See it in real stocks
Search US stocks on Stocklore to see Market and other financial metrics alongside the sector average.
This explanation is for information and reference only and is not a recommendation to buy or sell any security. Investment decisions and their consequences are your own.