Market capitalisation is the total market value of a company's outstanding shares. It's used to classify companies by size: mega-cap (>$200B), large-cap ($10-200B), mid-cap ($2-10B), small-cap ($300M-2B), micro-cap (<$300M).
Market Cap = Current Share Price × Total Shares Outstanding
A company with 1 billion shares outstanding at $150 per share has a market cap of $150 billion (large-cap). Apple at ~$3 trillion is a mega-cap.
AllInvestView displays market cap on stock detail pages. Compare valuations using PE Ratio and Price-to-Book.