Market capitalization (market cap) is the total value assigned to a publicly traded company by the stock market. It is calculated by multiplying the current share price by the total number of shares outstanding.
Market cap is the primary metric used to size companies. The largest companies in the world — Apple, Microsoft, Nvidia — each have market caps exceeding $2–3 trillion. Market cap categories: Large-cap ($10B+), Mid-cap ($2B–$10B), Small-cap ($300M–$2B), Micro-cap (under $300M).
A billionaire's personal net worth is closely tied to market cap when they hold a significant ownership stake in a company. A 10% stake in a $100B company means $10B in personal wealth from that holding alone.