What is market cap?
Market capitalisation (market cap) is the simplest measure of a company's total size in the eyes of the stock market:
Market Cap = Stock Price × Total Shares OutstandingApple trades at ~$185 with ~15.3 billion shares outstanding → market cap ≈ $2.8 trillion. That's what the market says the entire company is worth today.
The market cap categories
Investors divide stocks into groups by market cap because each group has different characteristics:
| Category | Range | Characteristics |
|---|---|---|
| Mega-cap | >$200B | Global brands, highly liquid, move markets |
| Large-cap | $10B–$200B | Established, dividend payers, lower volatility |
| Mid-cap | $2B–$10B | Growth potential with some stability |
| Small-cap | $300M–$2B | Higher growth potential, higher risk |
| Micro-cap | <$300M | Speculative, illiquid, high failure rate |
Why market cap matters for your portfolio
Diversification by size. Large-cap and small-cap stocks don't always move together. Adding exposure across the size spectrum reduces concentration risk.
Liquidity. Large-caps trade millions of shares daily. You can buy and sell without meaningfully moving the price. Small-caps can be illiquid — a large order can spike or crash the price.
Index membership. The S&P 500 requires a minimum market cap of ~$14B (as of 2024). When a stock enters or exits an index, billions of dollars in index funds must buy or sell — which moves the price.
Market cap vs. enterprise value
Market cap only counts equity. But a company with $5B in market cap and $10B in debt is far more expensive to actually acquire than one with $5B in market cap and $5B in cash.
Enterprise Value (EV) = Market Cap + Total Debt − Cash
EV is used in EV/EBITDA, EV/Revenue, and similar ratios that properly account for capital structure. For companies with significant debt (utilities, telcos, financials), EV-based ratios are more meaningful than P/E or market cap alone.
The float vs. market cap distinction
"Float" is the number of shares actually available for trading (excludes insider-held, restricted, and treasury shares). A company with 1 billion shares outstanding but 600 million locked up has a float of only 400 million shares — making it more susceptible to price swings on modest volume.
Our stock analysis tool shows market cap, enterprise value, and float for every major US stock alongside our quant factor scores.
Key takeaways
- Market cap = stock price × shares outstanding. It's the market's total valuation of the company.
- Large-cap = stability and liquidity; small-cap = higher growth potential and risk.
- Market cap ignores debt — use enterprise value for acquisition-cost comparisons.
- Index membership and rebalancing flows are driven by market cap thresholds.