How is market capitalisation calculated?

Multiply the current share price by the total number of outstanding shares. For example, a company with 1 billion shares trading at £5 each has a market cap of £5 billion.

What is a large-cap stock?

Generally, companies with a market cap above £10 billion. In the UK, these are typically FTSE 100 constituents — household names like Shell, AstraZeneca, and HSBC.

Does a high share price mean a large company?

No. Share price alone is meaningless for comparing company sizes. A company with a £1,000 share price and 1 million shares (£1bn market cap) is much smaller than one with a £10 share price and 1 billion shares (£10bn market cap).

Why does market cap matter for investors?

Market cap helps you understand the size and risk profile of a company. Larger companies tend to be more stable but grow more slowly. Smaller companies can grow faster but are more volatile and have higher failure rates.

What are the FTSE size indices?

FTSE 100 = largest 100 UK companies. FTSE 250 = next 250 (mid-cap). FTSE SmallCap = smaller companies below the top 350. FTSE AIM = companies on the Alternative Investment Market.

Can market cap be misleading?

Yes. Market cap does not account for debt. A company with a £5bn market cap but £4bn in debt has a very different financial position from one with £5bn market cap and no debt. Enterprise value (market cap + debt - cash) is often more informative.

Market Capitalisation Explained: What It Tells You

What Is Market Capitalisation?

Market capitalisation (market cap) is the total market value of a company's outstanding shares. It is calculated by multiplying the current share price by the total number of shares in circulation.

Market Cap = Share Price × Shares Outstanding

For example, if a company has 500 million shares trading at £20 each, its market cap is £10 billion.

Size Classifications

Companies are broadly categorised by their market cap:

Large-cap (£10bn+): Established, stable companies with global operations. Examples: Shell, Unilever, AstraZeneca. Lower risk, moderate growth potential.
Mid-cap (£2bn–£10bn): Growing companies with established market positions. Often found in the FTSE 250. Balance of growth and stability.
Small-cap (£300m–£2bn): Younger or niche companies with significant growth potential but higher volatility and risk.
Micro-cap (under £300m): Very small companies, often on AIM. Highest growth potential but also highest risk of failure.

Why Market Cap Matters

Market cap helps investors in several ways:

Size comparison: Compare companies objectively regardless of share price
Risk assessment: Larger companies are generally more stable; smaller ones more volatile
Index eligibility: Determines inclusion in FTSE 100, FTSE 250, etc.
Portfolio construction: Helps balance exposure across company sizes

AI trading bot analysing market data with neural network patterns — AI-powered tools are increasingly used to identify market patterns and automate trades.

Share Price vs Market Cap

One of the most common beginner mistakes is thinking a high share price means a company is large or expensive. This is incorrect.

Berkshire Hathaway's Class A shares trade at over $600,000 each, but it is not the world's largest company. Apple, with shares around $170, has a much higher market cap because it has far more shares outstanding.

Always use market cap — not share price — when comparing company sizes.

UK Market Context

The FTSE indices are constructed entirely by market cap:

FTSE 100: The 100 largest UK-listed companies by market cap (reviewed quarterly)
FTSE 250: Companies ranked 101st to 350th by market cap
FTSE All-Share: Combines the FTSE 100, 250, and SmallCap indices

Limitations of Market Cap

Market cap has important limitations:

It ignores debt — two companies with identical market caps can have vastly different financial health
It reflects market sentiment, not necessarily fundamental value
It can be inflated by hype or depressed by fear
Enterprise value (market cap + net debt) often provides a more complete picture