There are many more stocks in the S&P 500 than in the DOW. The DOW or the Dow Jones Industrial Average is an index that contains the 30 largest stocks in the market. The 30 stocks in the DOW are also in the S&P 500 index. The main difference between the two indexes is that the S&P 500 is a float-adjusted market-cap-weighted index. In other words, the stocks in the S&P 500 are weighted based on market value instead of their stock prices. The market cap is calculated by multiplying the stock's price by the number of outstanding shares, adjusted for a public float. The public float is the number of shares available to the public. They do it this way to ensure that a 10% change in a $20 stock will affect the index the same way a 10% change in a $50 stock affects it. The Dow Jones Indices is a price-weighted index. Because of this, price changes in the higher-priced stocks will have a more significant impact on the DOW level than price changes in lower-priced stocks. The S&P 500 is more meaningful than the handful of 30 stocks on the Dow Jones Indices when watching the daily market.