Walk into any investing conversation and someone will call a Rs 3,000 stock expensive and a Rs 40 stock cheap. The share price alone tells you almost nothing about how big or how expensive a company actually is.
Market capitalisation, shortened to market cap, fixes this. The formula is share price multiplied by the total number of shares outstanding. That single number is what the stock market collectively thinks the entire company is worth right now, today.
Reliance Industries had roughly 677 crore shares outstanding in early 2024, trading at around Rs 2,900 per share (as of early 2024). Multiply those and you get a market cap of close to Rs 20 lakh crore. That makes Reliance the most valuable listed company in India, ahead of TCS, HDFC Bank, Infosys, and every other name you can think of. Not because its share price is the highest, but because the total value of all its shares outstanding is the largest.
Why share price tells you nothing on its own
Take a company trading at Rs 5,000 per share with only 10 lakh shares in existence. Market cap: Rs 500 crore. Now take another company at Rs 50 per share but with 100 crore shares outstanding. Market cap: Rs 5,000 crore. The Rs 50 stock is a company ten times larger than the Rs 5,000 stock. Infosys had about 414 crore shares outstanding as of March 2024, trading at around Rs 1,500, giving it a market cap of roughly Rs 6 lakh crore — a third of Reliance's, despite the share prices looking vaguely comparable. Investors who treat a low share price as a signal of cheapness are missing the entire picture.
This is also why stock splits are mostly cosmetic. When Infosys split its shares in the past, existing shareholders got more shares at a proportionally lower price. The market cap stayed identical. The business did not become more valuable. The stock did not become more accessible in any financial sense. Only the optics changed.
Large cap, mid cap, small cap
SEBI formally defines large-cap companies as the top 100 Indian stocks by market cap, mid-caps as ranks 101 to 250, and small-caps as rank 251 and below. In rough terms, large cap means market cap above roughly Rs 20,000 crore, mid cap between Rs 5,000 and Rs 20,000 crore, and small cap below Rs 5,000 crore. These thresholds drift as the overall market rises or falls.
The categories matter for a practical reason. Mutual funds have regulatory mandates to stay within specific market-cap buckets. A large-cap fund cannot just decide to put most of its money into small-cap stocks. So when a company moves from mid-cap to large-cap, funds focused on large caps have to buy it. And funds mandated to hold mid-caps have to sell it.
Zomato was added to the Nifty 50 index on March 28, 2025, replacing BPCL. Getting added to Nifty 50 meant every index fund and ETF tracking the index had to buy Zomato shares, creating billions of rupees of automatic demand on a single day. The stock moved significantly on the news not because the business changed, but because of what index inclusion forces fund managers to do.
What market cap does not tell you
Market cap is the market's current opinion about a company's value. Opinions, especially collective ones formed under euphoria or panic, can be badly wrong. Companies routinely trade at market caps that bear little relationship to what a rational buyer would pay for the underlying business.
The wave of new-age tech IPOs in 2021 is a clean example. Paytm listed at a market cap of around Rs 1.3 lakh crore in November 2021. Within a year it had lost over 75 percent of that market cap. The business did not fall off a cliff in twelve months. The market's initial opinion of what it was worth was simply wrong.
Market cap tells you what the market thinks today. A low market cap can mean an undervalued business, or it can mean a legitimately struggling one. A high market cap can reflect genuine quality, or it can reflect collective overoptimism. The number is the starting point for a question, not the answer to one.