Market cap explained

Large-cap, mid-cap, small-cap — and why size matters.

TL;DR

Market cap is share price multiplied by total shares outstanding — the public market's total valuation of a company. It's the single most important sizing metric in equities.

The formula

Market cap = Share price × Shares outstanding. Use diluted shares for a more honest figure (includes options that will likely become shares).

Size categories

Most professionals slice the market by cap because liquidity, volatility, and analyst coverage scale with size.

→Mega-cap: over $200B (AAPL, MSFT, NVDA)
→Large-cap: $10B–$200B (typical S&P 500 constituent)
→Mid-cap: $2B–$10B
→Small-cap: $300M–$2B (Russell 2000 territory)
→Micro-cap: under $300M — illiquid, often overlooked

Market cap vs enterprise value

Market cap only looks at equity. Enterprise value adds debt and subtracts cash — it's the true cost to acquire the whole business. For comparing companies with different debt loads, EV is more honest.

Worked example

Microsoft (MSFT) worked example

MSFT trades at $415, with 7.43 billion shares outstanding.

1Share price$415
2Shares outstanding7.43B
3Market cap$415 × 7.43B = ~$3.08T
4Cash≈$80B
5Debt≈$55B
6Enterprise value$3.08T − $80B + $55B ≈ $3.05T

Takeaway

MSFT sits comfortably in the mega-cap tier with one of the largest enterprise values on Earth.

Common mistakes

What to avoid

!Using market cap to judge cheapness — that's what P/E and EV/EBITDA are for
!Confusing market cap with revenue or assets — they measure different things
!Ignoring float (publicly tradable shares) — insider-heavy stocks can have small float and big spreads
!Comparing mega-cap returns to small-cap returns without adjusting for risk

Self-check

Test yourself

Q1Company X trades at $50 with 200M shares. What's its market cap?+

$50 × 200M = $10B (large-cap)

Q2Why does enterprise value matter more than market cap when comparing across debt levels?+

Because it includes the debt the acquirer would inherit.

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