S&P 500 vs Nasdaq-100 vs Dow: Market Cap, Index Weighting and Sectors Explained
Market Cap, Indexes & Sectors
Market cap is share price times shares outstanding. Indexes use it (or price) to decide how much each company counts. Enter three made-up companies to see how cap weighting and price weighting differ.
The three big US indexes
| Index | What's in it | Weighting |
|---|---|---|
| S&P 500 | About 500 large US companies chosen by a committee | Float-adjusted market cap |
| Nasdaq-100 | About 100 of the largest non-financial companies listed on Nasdaq | Modified market cap (caps on the largest weights) |
| Dow Jones Industrial Average | 30 large US blue-chip companies | Share price |
The 11 GICS sectors
- Information Technology
- Health Care
- Financials
- Consumer Discretionary
- Communication Services
- Industrials
- Consumer Staples
- Energy
- Utilities
- Real Estate
- Materials
- Size labels are loose: large cap is often over $10B, mid cap $2B–$10B and small cap under $2B.