Complete Guide to Market Cap
— Large, Mid, Small-Cap Characteristics and Index-Inclusion Criteria
Market Cap is the most basic yardstick for a company's size. We cover the large/mid/small-cap classification criteria, index-inclusion requirements, and the difference from share price, all in one place.
What Is Market Cap?
Market Capitalization is the current share price multiplied by the total shares outstanding — the market's valuation of the entire company.
Market Cap = Share Price × Shares Outstanding
Example: a $150 share price and 160-eok shares outstanding (roughly 16 billion) → a $2.4 trillion market cap (roughly Apple's figure). Even a $5 share price can add up to a trillion-dollar market cap if shares outstanding run into the billions.
Classification by Size
| Category | Market-Cap Threshold (US) | Flagship Index | Character |
|---|---|---|---|
| Mega Cap | $2,000-eok or more (roughly $200B+) | Top of the S&P 500 | Global giants like AAPL, MSFT, NVDA |
| Large Cap | $100-eok to $2,000-eok (roughly $10B–$200B) | S&P 500 | Stable dividends, low volatility |
| Mid Cap | $20-eok to $100-eok (roughly $2B–$10B) | S&P MidCap 400 | A balance of growth and stability, moderate analyst coverage |
| Small Cap | $3-eok to $20-eok (roughly $300M–$2B) | Russell 2000 | High growth potential, high volatility |
| Micro Cap | Under $3-eok (roughly $300M) | Russell Microcap | Low liquidity, pump-and-dump risk |
* Thresholds vary by index provider and get periodically readjusted with market conditions.
Comparing Characteristics by Size
| Item | Large Cap | Mid Cap | Small Cap |
|---|---|---|---|
| Volatility | Low | Medium | High |
| Liquidity | Very high | High | Low |
| Growth potential | Moderate | Medium to high | High (with more risk too) |
| Dividend tendency | High | Medium | Low (favors reinvesting for growth) |
| Analyst coverage | Extensive | Medium | Sparse (large information asymmetry) |
| Economic sensitivity | Low (defensive) | Medium | High (hit hard in a downturn) |
How Major Indices Relate to Market Cap
- S&P 500 — 500 large US stocks, market-cap weighted. Inclusion criteria: roughly $180-eok or more in market cap plus 4 consecutive profitable quarters
- Russell 2000 — 2,000 small US stocks. Reconstituted (rebalanced) every June, the benchmark small-cap index
- Nasdaq 100 — 100 tech/growth-focused names, market-cap weighted
- Dow Jones — 30 blue-chip stocks, price-weighted (not market-cap weighted — this creates a structural distortion)
Market Cap vs. Float
Shares outstanding includes shares held by insiders and institutions that don't actually trade in the market. The supply that's actually free to trade in the market is called the Float. A small float means the price can move a lot even on modest supply/demand — this is one reason small caps and low-float stocks are so volatile.
The Illusion of Market Cap vs. Share Price
"A low share price means it's cheap" is the most common misconception. A $1 stock with 100-eok shares outstanding (roughly 10B) has a $100-eok market cap (roughly $10B, a large cap). A $1,000 stock with 100-man shares outstanding (roughly 1M) has a $10-eok market cap (roughly $1B, a small cap). Always compare companies by market cap, never by share price.
Check It Right Now
On today's scan, you can check each stock's size alongside its technical signals. See also PER, PBR, ROE and EPS.