The price-to-earnings (P/E) ratio measures a company's share price relative to its earnings per share (EPS). Often called the price or earnings multiple, the P/E ratio helps assess the relative value of a company's stock. It's handy for comparing a company's valuation against its historical performance, against other firms within its industry, or the overall market.

P/E can be estimated on a trailing (backward-looking) or forward (projected) basis.