Market capitalization, usually shortened to market cap, is the quickest measure of how big a public company is: the price of one share multiplied by the number of shares in existence. It decides which index a stock can join, how much of an index fund's money flows into it and whether the news calls it a large or small company. Below you will find how to calculate it from a company's own filings, how index providers draw the lines between size tiers, how enterprise value brings debt into the picture and where the headline number misleads. For the wider basics of owning shares, start at the stocks hub.
What is market cap?
Market cap is the total market value of a company's shares: the current share price multiplied by the number of shares outstanding.
Market cap = share price × shares outstanding
Nvidia shows the arithmetic. Its 10-Q reported 24.1 billion shares outstanding as of August 21, 2026, and the stock closed at $204.64 on October 30, 2026. Multiply the two and the market valued its equity at about $4.93 trillion that day. Because the price changes with every trade, so does the result.
The figure is what investors in aggregate are paying for the shares at that moment, not an appraisal of the business, and on its own it says nothing about whether the stock is cheap or expensive. Comparing price with profit is the job of the P/E ratio. Market cap also ignores how a company is financed: two businesses with identical market caps can owe very different amounts, which is why enterprise value exists.
How do you calculate market cap when a company has several share classes?
Multiply each class by its own price and add the results, valuing any unlisted class at the price of the listed shares it converts into.
Worked example: Alphabet's market cap from its 10-Q cover, October 30, 2026
| Share class | Shares outstanding, October 21, 2026 | Price used | Market value |
|---|---|---|---|
| Class A (GOOGL), one vote per share | 5,888 million | $279.84 close | $1,647.7 billion |
| Class B (not listed), 10 votes, converts one-for-one into Class A | 827 million | $279.84, the Class A price | $231.4 billion |
| Class C (GOOG), no votes | 5,579 million | $278.22 close | $1,552.2 billion |
| Total | 12,294 million | $3,431.3 billion |
- Check: 5,888 × $279.84 + 827 × $279.84 + 5,579 × $278.22 = about $3.43 trillion
- The GOOGL line alone, $1,647.7 billion, is only 48% of the company's value
Alphabet's certificate of incorporation gives each Class B share ten votes and lets holders convert it into Class A at any time, which is why valuing it at the Class A price is the usual convention. Class C shares carry no votes but receive the same dividends, and on October 30 they closed within 0.6% of the Class A price. A quote page that shows the value of one ticker can understate a multi-class company badly, and rebuilding the figure from the 10-Q cover settles the question.
Which share count should you use?
Use the shares outstanding on the cover of the latest 10-Q or 10-K, a count that excludes stock the company has bought back and holds in treasury.
That cover figure is dated close to the filing, so it is usually more current than the balance sheet: Nvidia's count is as of August 21, 2026, while its balance sheet is as of July 26. Analysts sometimes prefer a diluted count, which adds shares that stock options, restricted stock units and convertible securities could create. For mature companies the gap is small; Microsoft's diluted weighted-average count for the quarter ended September 30, 2026 was 7,446 million against 7,426 million basic, a difference of about 0.3%. For young companies paying staff heavily in stock it can be much larger.
Share counts drift between filings. Buybacks shrink them and new issuance or employee awards expand them, so a data site using an old count can be off by a few percent. Splits change the count but not the total value, as stock splits explained shows.
What counts as large cap, mid cap and small cap?
There is no legal definition, so each index provider draws its own lines, and the dollar cutoffs move as the overall market rises or falls.
| Provider | Large or mega cap | Mid cap | Small cap | How the line is set |
|---|---|---|---|---|
| S&P Dow Jones Indices | S&P 500: at least $22.7 billion | S&P MidCap 400: $8.0 billion to $22.7 billion | S&P SmallCap 600: $1.2 billion to $8.0 billion | Dollar ranges aimed at the 85th, 93rd and 99th cumulative percentiles of US market value, reviewed each quarter |
| FTSE Russell | Russell 1000, above a breakpoint of about $5.7 billion | Russell Midcap, a subset of the Russell 1000 | Russell 2000, below the breakpoint, down to $146.4 million | Companies ranked by total market cap on rank day, April 30 in 2026 |
| CRSP | Mega cap: the largest companies making up 70% of market value; large cap: 85% | The slice from 70% to 85% | The slice from 85% to 98%, with micro caps beyond | Cumulative share of total market value, with bands to limit turnover |
S&P Dow Jones Indices currently requires a total company market cap of at least $22.7 billion for the S&P 500, $8.0 billion to $22.7 billion for the S&P MidCap 400 and $1.2 billion to $8.0 billion for the S&P SmallCap 600. Those are tests for joining. The methodology says the criteria apply to additions, not to continued membership, so a company that slips below the line is not removed for that alone. The other S&P 500 entry rules are covered in what is the S&P 500.
FTSE Russell's 2026 breakpoint between the large-cap Russell 1000 and the small-cap Russell 2000 was about $5.7 billion, up 24% in a year. A band of 2.5 percentile points either side of it limits switching, which is why the smallest Russell 1000 member was worth $2.7 billion and the largest Russell 2000 member $9.6 billion. From 2026 the Russell indexes are rebuilt twice a year, in June and December. CRSP takes a third approach, dividing by cumulative value rather than by a count of companies, and its own research notes that studies of company size find no distinct statistical breakpoints. Every cutoff is partly a convention.
How have the size cutoffs changed over time?
The cutoffs follow the market in both directions, rising through long rallies and falling after major declines.
| Effective date | S&P 500 minimum | S&P MidCap 400 range | S&P SmallCap 600 range |
|---|---|---|---|
| July 18, 2007 | $5.0 billion | $1.5 billion to $5.5 billion | $300 million to $2.0 billion |
| December 18, 2008 | $3.0 billion | $750 million to $3.3 billion | $200 million to $1.0 billion |
| February 16, 2011 | $4.0 billion | $1.0 billion to $4.4 billion | $300 million to $1.4 billion |
| March 10, 2017 | $6.1 billion | $1.6 billion to $6.8 billion | $450 million to $2.1 billion |
| February 20, 2019 | $8.2 billion | $2.4 billion to $8.2 billion | $600 million to $2.4 billion |
| March 4, 2022 | $14.6 billion | $3.7 billion to $14.6 billion | $850 million to $3.7 billion |
| January 4, 2023 | $12.7 billion | $4.6 billion to $12.7 billion | $750 million to $4.6 billion |
| January 2, 2025 | $20.5 billion | $7.4 billion to $20.5 billion | $1.1 billion to $7.4 billion |
| July 1, 2025 | $22.7 billion | $8.0 billion to $22.7 billion | $1.2 billion to $8.0 billion |
The S&P 500 minimum is about 4.5 times its 2007 level, yet it was cut to $3.0 billion during the financial crisis in December 2008 and lowered again in January 2023 after the 2022 decline. S&P reviews the ranges at the start of every quarter and considers an update when the implied ranges move by 10% or more. The practical point is that a company called large cap a decade ago might meet only the mid-cap test today without having shrunk at all.
What is float-adjusted market cap?
Float-adjusted market cap counts only the shares available for public trading, leaving out blocks held by founders, governments, parent companies and other long-term strategic owners.
Index providers weight their indexes this way. S&P Dow Jones Indices expresses the float as an investable weight factor between 0 and 1 and requires a factor of at least 0.10 for its S&P 500, MidCap 400 and SmallCap 600. A listed share line must also have a float-adjusted value of at least half the minimum company size, which at the current S&P 500 threshold works out to $11.35 billion.
Share classes add a twist. S&P judges eligibility on the whole company's total market cap, including unlisted classes, but weights each listed line only by its own float-adjusted value and never folds unlisted shares into a listed line. For Alphabet, the Class B shares count toward the company passing the size test, yet only GOOGL and GOOG carry index weight, each on its own float. The result is that a company with a large founder or government stake gets less index weight, and less index-fund buying, than its headline size suggests.
What is enterprise value, and how is it different from market cap?
Enterprise value estimates what it would cost to take over the whole business: market cap plus debt, minus the cash and liquid investments that could pay that debt down.
Worked example: Enterprise value for Nvidia and Verizon, October 30, 2026
| Line | Nvidia | Verizon |
|---|---|---|
| Share price, October 30 close | $204.64 | $44.73 |
| Shares outstanding | 24.1 billion | 4,145 million |
| Market cap | $4,931.8 billion | $185.4 billion |
| Plus total debt | $33.4 billion | $166.2 billion |
| Minus cash and marketable debt securities | $56.6 billion | $4.5 billion |
| Enterprise value | $4,908.6 billion | $347.1 billion |
| Enterprise value ÷ market cap | 0.995 | 1.87 |
- Balance sheet dates: July 26, 2026 for Nvidia and September 30, 2026 for Verizon
- Verizon: $185.4 + $166.2 − $4.5 = $347.1 billion
By market cap Nvidia was about 27 times the size of Verizon; by enterprise value, about 14 times. Verizon's debt is nearly as large as the market value of its shares, so a buyer of the whole company would take on almost as much in borrowings as it paid for the stock. Nvidia's cash more than covered its debt, leaving its enterprise value slightly below its market cap, and lower still if you also subtract the $42.8 billion of marketable shares it held in other companies, a step some analysts take and others skip.
Definitions vary in other ways as well. Some versions add preferred stock, minority interests or lease obligations, so compare enterprise values only when they are built the same way. Ratios such as enterprise value to sales or to operating profit let you compare companies with very different balance sheets, something a P/E cannot do.
How concentrated is the US stock market?
A handful of companies account for a large share of total US market value, which shapes every index weighted by market cap.
| Group on April 30, 2026 | Total market cap | Share of the Russell 3000 |
|---|---|---|
| Ten largest companies | $26.4 trillion | About 35% |
| Apple, Microsoft, Nvidia, Amazon, Alphabet, Meta and Tesla | $22.4 trillion | About 30% |
| Russell 1000 | $72.1 trillion | About 95% |
| Russell 2000 | $3.5 trillion | About 5% |
| Russell 3000 | $75.6 trillion | 100% |
FTSE Russell's rank-day figures show how lopsided the distribution has become. Nvidia, the largest company, was valued at $4.85 trillion, more than every member of the Russell 2000 put together. Ten companies were worth more than $1 trillion, up from seven a year earlier, and Apple, third on the list at $3.98 trillion, is tracked on Apple's stock page. The combined value of the ten largest rose 47.8% in a year, from $17.9 trillion to $26.4 trillion.
In an index weighted by market cap, each dollar is split in proportion to company size, so a broad fund built this way ties roughly a third of its value to ten companies when concentration is at this level. How such funds are built is covered in index funds explained.
How fast can a company's market cap change?
Market cap moves with every trade, and for the largest companies a single earnings report can shift it by hundreds of billions of dollars in days.
Alphabet released its third-quarter results on October 28, 2026. Over the next two sessions its Class A shares fell from $324.89 to $279.84 and its Class C shares from $321.89 to $278.22. Applying the same 10-Q share counts, total market cap went from about $3.98 trillion to $3.43 trillion, a drop of roughly $546 billion, or 13.7%, nearly three times Verizon's entire market value.
None of Alphabet's buildings, servers or cash disappeared in those two days. What changed was the price investors were willing to pay for a share of its future profits, which is the sense in which market cap is a running opinion rather than a measurement. What to look for in the report behind such a move is covered in how to read an earnings report.
What are the risks of judging a company by its market cap?
Market cap describes size, not quality or value, and treating it as more than that leads to several common mistakes.
- Size is not cheapness. A $4 trillion company can be expensive and a $2 billion company cheap; only earnings, cash flow and growth answer that question.
- Debt is invisible. Verizon's market cap understated what its business would cost a buyer by almost half, and a P/E built on market cap inherits the same blind spot.
- Cap-weighted funds concentrate. Owning the broad market through a cap-weighted fund means owning a lot of a few companies, so their setbacks hit the whole portfolio.
- Small companies trade thinly. Fewer shares change hands and bid-ask spreads are often wider, which raises the cost of getting in and out; how to read a stock quote explains the spread.
- Crossing a breakpoint forces trades. When companies move between size indexes, funds tracking them must buy or sell. FTSE Russell reports $217.2 billion traded at the close of its June 2025 reconstitution.
- Counts go stale. Buybacks, new issuance and unlisted share classes can leave a published market cap several percent, or in Alphabet's case far more, away from the real figure.
Size is also one axis of the familiar style grid, with growth and value on the other, compared in growth vs value investing. The difference between valuing a company from its accounts and reading its price chart is in fundamental vs technical analysis.