Market Capitalization
Capitalisation boursière in French
Quick definition
Market capitalization is the total value the market puts on a company: the share price multiplied by the number of shares outstanding. It measures a company's size, and it decides how much of each company most index funds hold.
Price times shares
The formula could not be simpler: market cap = share price x shares outstanding. A company with 200 million shares trading at $40 has a market cap of $8 billion. That is what it would cost, in theory, to buy every share of the stock at today's price.
The formula also exposes a common beginner trap: the share price alone says nothing about a company's size. A $400 stock can belong to a small company that issued few shares, and an $8 stock can belong to a giant that issued billions of them. Size lives in the multiplication, never in the price.
Large cap, mid cap, small cap
Investors sort companies into size buckets: large cap for the giants, mid cap for the middle tier, small cap below that, and micro cap for the smallest listings. The boundaries are conventions rather than official rules, they drift over time, and a large cap in Canada might only qualify as a mid cap by US standards. Treat the labels as rough neighbourhoods, not legal categories.
The labels still carry real information. Larger companies tend to be more established, more widely analyzed, and much easier to trade in volume; smaller companies tend to be less proven and less liquid, with more room to grow and more ways to disappoint. Tend is the operative word in both directions.
What market cap does and does not tell you
Market cap tells you two things well: how big a company is relative to others, and how much weight it will carry in an index. It does not tell you whether the company is cheap or expensive, well run or fragile: a huge market cap can be attached to an overpriced business, and a small one to a bargain. Size is not a verdict on value, and it is not a guarantee of safety.
One soft caveat for the curious: market cap counts only the equity. A company's debts matter too, which is why professionals valuing a whole business look at enterprise value, a measure that starts from market cap and accounts for debt and cash. For everyday investing, knowing that the distinction exists is enough.
Cap-weighted indexes: why this number runs your portfolio
Here is where market cap stops being trivia. Most index funds and ETFs weight their holdings by market cap: a company worth twice as much gets twice the weight. Buy a broad index fund and you automatically own more of the biggest companies and less of everyone else, with the weights updating themselves as prices move, no trading required.
The modern consequence is concentration. When a few giant companies grow much faster than the rest, cap weighting steadily hands them a larger share of the index, and in recent years a handful of the world's largest firms have come to represent a striking share of broad global and US indexes. The Canadian version of the same story is sectoral: the TSX leans heavily toward banks and energy, so a Canadian index fund is far more concentrated in a couple of industries than the word "index" suggests. None of this makes cap weighting wrong; it has low costs and a clean logic. It does mean an index fund is not automatically the last word in diversification, which is one reason to spread across markets rather than relying on a single country's index.
In Canada
The entire Canadian stock market represents only a few percent of world market capitalization, and even Canada's largest companies are mid-sized by global standards. Size labels are therefore relative to the market you are standing in: a TSX heavyweight can be a modest position in a global index fund.
The size split is also institutional in Canada: established companies list on the Toronto Stock Exchange, while the smallest public companies trade on the TSX Venture Exchange, where tiny market caps, thin trading and speculative pricing are the norm.
Worked example
Company A has 50 million shares at $120: a market cap of $6 billion. Company B has 2 billion shares at $8: a market cap of $16 billion. Despite the humble-looking share price, B is nearly three times the size of A.
Now put both into a cap-weighted index. B receives almost three times A's weight, so an investor holding an index fund tracking that index owns almost three times as much of B, without ever having made that decision. Multiply this across hundreds of companies and you have the quiet machinery inside nearly every index portfolio.
Related terms
Reviewed by Alexandre Bernier, CFP®, CIM®, PFP®·Updated August 2026