Beta Sizing is a method used in finance to measure the sensitivity of an investment's returns to market movements. It helps investors understand how much a stock or portfolio might move in relation to a benchmark index, such as the S&P 500. A beta greater than 1 indicates higher volatility than the market, while a beta less than 1 suggests lower volatility. This concept is crucial for portfolio management, as it aids in assessing risk. Investors can use beta to balance their portfolios according to their risk tolerance, ensuring they align their investments with their financial goals and market expectations.