Beginner
What It Means
Market cap tells you what the market thinks a company is worth. It’s calculated by multiplying the stock price by the total number of shares outstanding.Example
Both companies have the same market cap despite very different share prices. Share price alone doesn’t tell you company size.
Size Categories
Why It Matters
Market cap determines:- Which indices include a stock (S&P 500, Russell 2000, etc.)
- How much of an index a stock represents
- Liquidity and trading characteristics
- Risk and return expectations
Advanced
Market Cap vs. Other Size Measures
Float-Adjusted Market Cap
Most indices use float-adjusted market cap:- Insider holdings (executives, founders)
- Government holdings
- Strategic holdings by other companies
- Restricted stock
Index Weighting
Market cap determines portfolio weights in cap-weighted indices:Cap-weighted indices are “self-rebalancing” - as stocks rise, their weight naturally increases. No trading required to maintain weights.
The Size Factor
Academic research documents the “size premium” - historically, smaller companies have outperformed larger ones:Market Cap Characteristics by Size
Dynamic Nature
Market cap changes continuously:- Stock price movements
- Share buybacks (reduces shares, may increase price)
- Stock issuance (increases shares, may decrease price)
- Stock splits (no effect on market cap)
Sector Distribution by Size
Different sectors dominate different size segments:Limitations
- Price-Based: Reflects market sentiment, not intrinsic value
- Volatile: Can change dramatically with price swings
- Debt-Blind: Doesn’t account for leverage (use Enterprise Value)
- Industry Differences: Hard to compare across sectors
Related Terms
Beta
Small caps typically have higher beta
Factor Investing
Size is a key factor
Diversification
Across size segments