What Is Market Capitalization?

Market capitalization (market cap) is the total value the stock market puts on a company.

Market cap = share price × number of shares outstanding

If a company has 100 million shares trading at $50, its market cap is $5 billion. It’s the price you’d pay, in theory, to buy the whole company at today’s share price.

Size categories

• Mega cap — over $200 billion (Apple, Microsoft)
• Large cap — $10–200 billion
• Mid cap — $2–10 billion
• Small cap — $300 million – $2 billion
• Micro cap — under $300 million

Bigger companies tend to be more stable and widely followed; smaller ones can grow faster but swing harder and trade less. Market cap is the starting point for most valuation multiples, like P/E and price-to-sales — both are just market cap divided by a measure of business size. Filter by market cap in the screener .