Market capitalisation, or market cap, is the total market value of a company's shares: the share price multiplied by the number of shares outstanding. A company with 100 crore shares at Rs 1,500 each has a market cap of Rs 1.5 lakh crore. SEBI uses market cap rank to sort listed companies into large caps (top 100), mid caps (101 to 250) and small caps (251 onwards). Reliance Industries is the largest Indian company, at around Rs 18 lakh crore in mid-2026.
Market capitalisation is the price the stock market puts on a whole company. It is calculated by multiplying the current share price by the total number of shares the company has issued. The number changes every second the market is open, because the share price does. It is the most common way to describe how big a listed company is, and it drives everything from index membership to which mutual funds are allowed to buy the stock.
How it is calculated
Take a company with 100 crore shares outstanding and a share price of Rs 1,500. Its market cap is Rs 1.5 lakh crore. If the price rises to Rs 1,650, market cap is Rs 1.65 lakh crore, with nothing else about the company having changed. Share count matters as much as price. A stock trading at Rs 50 can belong to a bigger company than one trading at Rs 5,000, if it has many more shares. Price alone says nothing about size.
There are two versions. Full market cap uses all shares. Free-float market cap counts only the shares available for public trading, leaving out promoter holdings, government stakes and locked-in shares. The Nifty 50 and Sensex both weight their members by free float, which is why a company with a large promoter holding has less index weight than its full market cap would suggest.
Large, mid and small caps
SEBI defines the three buckets by rank, not by a rupee cut-off. The top 100 companies by average full market cap over the previous six months are large caps. Ranks 101 to 250 are mid caps. Rank 251 onwards is small cap. AMFI publishes the list every six months and mutual funds have to follow it. A large-cap fund must keep at least 80% of its money in the top 100, so a company that drops out of the top 100 can see funds forced to sell it. The characteristics of each group are compared in small cap vs mid cap stocks in India.
In practice the cut-offs sit around Rs 1 lakh crore for large caps and Rs 30,000 crore for mid caps, though both lines move with the market. Blue chips are almost always large caps, but the reverse is not true. A large cap is simply big, and big companies can still be badly run.
India's biggest companies
Reliance Industries has been the largest Indian company by market cap for most of the past decade, at about Rs 18 lakh crore in mid-2026. HDFC Bank, TCS, Bharti Airtel and ICICI Bank fill out most of the top five. The combined market cap of all companies listed on BSE crossed 5 trillion dollars in mid-2026, which puts India among the four or five largest stock markets in the world. The size and weight of these companies are what the broader index guides cover, including the full guide to the mid-cap indices.
What market cap tells an investor
Size is a rough guide to risk. Large caps are more stable, more liquid and more closely followed. Small caps grow faster when things go well and fall harder when they do not. Market cap also sets the floor for liquidity: a company worth Rs 500 crore cannot absorb a Rs 50 crore order without the price moving. And it is the starting point for valuation. Divide market cap by net profit and the result is the P/E ratio. Add net debt to market cap and the result is enterprise value, used in comparable company analysis.
What it does not tell
Market cap is not what a company is worth in any fundamental sense. It is what the market is paying right now, and the market can be wrong in both directions. It is not the same as the value of the company's assets, nor the amount of money the company has. A company can have a market cap of Rs 1 lakh crore and Rs 50 crore in the bank. Market cap rank also changes constantly, so a stock can move from mid cap to large cap and back within a year.
FAQs
Does a stock split change market cap?
No. A split doubles the share count and halves the price, so market cap stays the same.
What is a mega cap?
An informal label for the very largest companies, usually those above Rs 5 lakh crore in India. SEBI does not define it.
Why does market cap matter for mutual funds?
SEBI rules tie fund categories to the market cap ranking, so a large-cap fund, a mid-cap fund and a small-cap fund each have to buy from the right bucket.
How is market cap different from enterprise value?
Enterprise value adds net debt to market cap. It is the price of buying the whole business, debts included.