In the spirit of better investing, and in celebration of the first annual Worldwide Invest Better Day (WWIBD) coming up on September 25, Motley Fool analysts will be answering user- and reader-submitted questions leading up to the big event. "Ask a Fool" anything, and we'll do our best to help you invest better.

Market cap is one of the many metrics that investors can use to assess the size of a company. One share of the biggest company in the world, Apple (NASDAQ:AAPL), currently costs $668. To calculate Apple's market cap, simply multiply that number by the number of shares outstanding -- in this case, around 943 million -- and you get a market cap of roughly $630 billion. Watch the video below to learn more about calculating and interpreting a company's market cap.


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