Market capitalization (market cap) is the total dollar value of a company's outstanding shares. It equals share price × diluted shares outstanding. For example, a company with 100 million shares trading at $50 has a $5 billion market cap. This is the market's current valuation of the equity, not the whole company (which includes debt). Market cap determines size classifications: mega-cap (>$200B), large-cap ($10B-$200B), mid-cap ($2B-$10B), small-cap ($300M-$2B), micro-cap (<$300M). Larger caps tend to be more liquid and less volatile.