Market capitalization: formula, free float and enterprise value

Market capitalization, usually shortened to market cap, is what the stock market says a company's equity is worth: the share price multiplied by the number of shares. It is the first number investors use to size up a company, the basis for how most indexes weight their members, and the dividing line between "large cap" and "small cap" funds.

The formula fits on one line, but each half of it hides decisions. Which shares count? What about shares employees could receive next year, or the half of a company its founder will never sell? And because market cap measures only the equity, it says nothing about the debt a buyer would also take on. This guide works through each of those questions with numbers, then looks at real market caps from October 2026 and the measure professionals use alongside it, enterprise value.

The formula and where the inputs come from

The price is easy: it is the latest trade, and it changes all day. The share count is slower-moving and comes from the company itself. US public companies report shares outstanding on the cover of every 10-Q and 10-K they file with the SEC, as of a recent date. Data providers pick that number up and multiply it by the live price. Between filings, buybacks and new share issuance quietly change the true count, so a quoted market cap can be slightly out of date even when the price is current.

Basic versus diluted shares

Basic shares outstanding are the shares that exist today. Diluted shares add those that could be created from employee stock options, restricted stock units and convertible securities. For companies that pay heavily in stock, the difference matters.

Quote screens almost always show the basic figure. Analysts valuing a company usually prefer diluted.

Companies with more than one share class

Some companies list two or more classes of shares, often with different voting rights. Alphabet's Class A (GOOGL) and Class C (GOOG) shares both trade on Nasdaq. Market cap is a company-level number, so a correct figure adds every class together, including any unlisted class, each at its own price or an equivalent. That is why the market cap shown next to GOOGL and next to GOOG is roughly the same total, not half each. Adding the two quotes together would count the company twice.

Free float: the shares that actually trade

Not every share is available to investors. Founders, family trusts, governments, parent companies and other strategic holders may own large blocks they are unlikely to sell. The free float is the portion left for the public to trade.

In the figure, insiders hold 300 million of 1,000 million shares. The float factor is 0.7, so at $40 the float-adjusted market cap is 1,000 million × $40 × 0.7 = $28 billion, against a full market cap of $40 billion.

Index providers weight by the float-adjusted figure because an index fund can only buy shares that are for sale. Weighting by the full market cap would force funds to chase a supply of stock that doesn't exist.

Low float also matters to individual investors. A stock with a small float can move violently on modest buying or selling, and recent IPOs often have small floats until lock-up agreements expire and insiders become free to sell.

Size categories

Investors sort companies into mega, large, mid, small and micro cap buckets. The labels are conventions, not regulations, and the boundaries differ by provider and drift upward as markets grow. Two widely used systems define size by membership rather than by a fixed dollar line:

• S&P Dow Jones Indices splits the US market into the S&P 500 (large cap), S&P MidCap 400 and S&P SmallCap 600. Since July 2025 a company added to the S&P 500 needs an unadjusted market cap of at least $22.7 billion; the MidCap 400 range is $8.0 billion to $22.7 billion and the SmallCap 600 range $1.2 billion to $8.0 billion. S&P reviews these ranges quarterly.
• FTSE Russell ranks every eligible US company by total market cap. The largest 1,000 form the Russell 1000 (large and mid cap) and the next 2,000 the Russell 2000 (small cap). The dollar breakpoint between them is whatever the 1,000th company happens to be worth on rank day, which for the December 2026 reconstitution was October 30, 2026.

So a "small cap" today may be bigger than a "large cap" was twenty years ago. When you compare funds, check which definition each uses rather than relying on the label.

Real market caps at the end of October 2026

The table uses Finabase quote data at the regular-session close of Thursday, October 29, 2026. The share count is implied by dividing market cap by price.

The table is a selection of very large US-listed companies, not a complete ranking. Two things stand out. Microsoft has the highest share price and only the third-largest market cap, because it has about half as many shares as Apple. And Broadcom trades at almost the same price as Apple but is worth about a third as much. Share price alone ranks nothing.

Enterprise value: what the whole business costs

Market cap prices the equity. A buyer of the entire company would also take on its debt and get its cash. Enterprise value (EV) captures both.

In the figure's example, a $40 billion market cap plus $12 billion of debt minus $7 billion of cash gives an EV of $45 billion.

That is why valuation multiples that compare against operating results before interest, such as EV/EBITDA or EV/sales, use enterprise value, while per-share measures such as the price-to-earnings ratio use market cap. Mixing them, for example dividing market cap by EBITDA, makes indebted companies look cheaper than they are.

Common mistakes with market cap

Treating it as cash value. Market cap is a price for the shares at the margin, set by the last trade. Nobody could sell every share at that price; trying to would push it down.

Ignoring the date of the share count. After a large buyback or share issuance, the quoted market cap can lag the true figure until the next filing.

Comparing across share classes carelessly. As with Alphabet, adding the market caps shown next to two share classes of the same company counts it twice.

Forgetting debt. A heavily indebted company can look small by market cap and large by enterprise value. For lenders and acquirers, EV is the relevant size.

Reading size as safety. Large companies are usually more diversified and more liquid, but they can and do fall sharply. Size describes a company; it doesn't guarantee anything.

Size measures compared

How Finabase helps

The quote on every symbol page shows Mkt cap next to price, volume, P/E and EPS. The screener runs screens across thousands of stocks and can sort the results by market cap, so the biggest or smallest names rise to the top. The heatmap draws the S&P 500 grouped by sector and industry with each company's tile sized by its market value, a quick way to see how much of the index a handful of companies represent.

For how cap weighting shapes the indexes, see Stock market indexes: S&P 500, Dow, Nasdaq and Russell explained. For what a share represents in the first place, see What is a stock? A complete beginner’s guide to shares.

Frequently asked questions

How do you calculate market cap?

Multiply the current share price by the number of shares outstanding. A company with 2 billion shares trading at $50 has a market cap of $100 billion.

Does a higher share price mean a bigger company?

No. Size depends on price and share count together. At the October 29, 2026 close, Apple's shares cost $348.91 and Nvidia's $213.66, yet Nvidia's market cap was slightly larger because it had about 24 billion shares to Apple's 15 billion.

What is the difference between market cap and enterprise value?

Market cap values only the shareholders' equity. Enterprise value adds the company's debt and subtracts its cash, approximating what it would cost to buy the whole business free of its obligations.

What is free float?

The shares available for the public to trade, excluding blocks held by insiders, founders, governments or parent companies. Indexes weight members by float-adjusted market cap because those are the shares funds can actually buy.

Summary

Market cap multiplies a share price by a share count to value a company's equity, and both inputs need care: the count comes from SEC filings, can be basic or diluted, and must cover every share class. Indexes adjust it for free float, so only tradable shares carry weight. Size buckets such as large and small cap are moving conventions defined by index providers, not fixed lines. And because market cap ignores debt and cash, enterprise value is the better measure of what a whole business costs. Used together, they turn a share price into a picture of how big a company really is.