Market Capitalisation

Market capitalisation is a company's share price multiplied by its number of shares outstanding: the market's total price tag on the business. A company with one billion shares at $10 is a $10 billion company. A company with 100 million shares at $50 is a $5 billion company, and the $10 share is the bigger business. The share price alone says nothing about size - the price is a ratio, and the share count is the other half of it.

The size matters because the index is built on it. The S&P/ASX 200 weights its members by market capitalisation, which means the largest companies dominate. The biggest bank alone is roughly a tenth of the index, and the banks and miners together are roughly half. Size also sorts the market into large, mid and small caps - a loose taxonomy the ASX uses for its indices and every fund uses for its label.

The arithmetic is one multiplication, updated every minute the market trades. Shares outstanding multiplied by the price is the market cap, and it moves with the price while the share count usually stands still. Company A: one billion shares at $10 is $10 billion. Company B: 100 million shares at $50 is $5 billion - the cheaper-looking share is half the company, because the count is the other half of the ratio.

The index is the second mechanism. The S&P/ASX 200 ranks its members by market cap and weights them proportionally, so the largest companies set the index's direction: the biggest bank is roughly a tenth of the index alone, and a 1 percent move in it moves the index by roughly a tenth of a percent. The diversification entry covers why the concentration matters - buying the index is buying the banks twice.

The valuation tie closes the mechanism. A $1 share can be expensive and a $400 share can be cheap, because the price means nothing without the earnings behind it: the price-to-earnings ratio divides the price by the earnings per share, and the share count is already inside both. The penny stock at $0.50 with two billion shares outstanding is a $1 billion company - the price is the sticker, the market cap is the car.

For an Australian reader, market cap is the number behind every index fund, every large-cap label and every concentration argument in Australian markets. The ASX 200 is weighted by market cap, which is why the banks and miners are roughly half of it - the share market index entry covers the index arithmetic. MoneySmart's guidance on shares treats company size as a risk factor: small caps move further in both directions, and large caps move the index.

A colleague named Brent (yes, that Brent) judged companies by share price alone and bought the $4 stock over the $40 one because it was "cheaper". The $4 stock had 200 million shares and a $800 million market cap; the $40 stock had two billion shares and an $80 billion cap. He compared the stickers and missed the cars. The highest-leverage thing most Australians can do is read the market cap before the price, and remember that buying the index is buying the largest companies by construction.