Estimating a Company's Market Cap From Scratch

"Estimate the market cap of a mid-sized streaming company with about 80 million subscribers, without looking anything up." This tests whether you can chain revenue-scale reasoning into a valuation, which is a different skill from the volume and headcount Fermi chains elsewhere in this section — it requires an extra step converting earnings into a market value using a multiple, and that multiple is itself an estimate you have to defend.

The decomposition

$$\text{market cap} \approx \text{users} \times \text{revenue per user} \times \text{net margin} \times \text{P/E multiple} .$$

In plain English: revenue per user times users gives total revenue; multiplying by net margin gives net income (earnings); multiplying earnings by a price-to-earnings multiple converts a flow of profit into a lump-sum valuation the market is willing to pay for owning a claim on that profit stream, going forward. Each factor is a separate anchor: revenue per user for a subscription streaming service is roughly its monthly subscription price times 12, so $12/month → $144/year; net margin for a maturing streaming business might be in the 10–15% range once content costs are under control; P/E multiple for a moderate-growth media/tech company might reasonably sit around 20–30x.

Worked example

Using 80 million users, $144/year revenue per user, 12% net margin, and 25x P/E: revenue $= 80 \times 144 = 11{,}520$ million, i.e. $11.5 billion; net income $= 11.5 \times 0.12 = 1.38$, i.e. $1.38 billion; market cap $= 1.38 \times 25 = 34.5$, i.e. $34.5 billion. Each step compounds the uncertainty of the last, so the honest answer to "what's the market cap" is a range — call it $25–45 billion — rather than a single precise figure, since a P/E anchor alone could easily be 20 or 35 depending on growth expectations the question didn't specify.

A cross-check from the revenue side alone

If you're less confident in the margin and multiple assumptions than in the revenue estimate, a useful shortcut is price-to-sales instead of P/E: mid-sized tech/media companies often trade at 2–4x revenue. Applying that directly to the $11.5 billion revenue figure gives $11.5 \times 3 \approx 34.5$, i.e. $34.5 billion — landing on almost exactly the same number as the P/E route, because a price-to-sales multiple of 3x and a P/E of 25x at a 12% margin are roughly consistent with each other ($25\times0.12=3$). This is a useful check: if your two routes give wildly different answers, your margin, P/E, and price-to-sales anchors are internally inconsistent even if each looks reasonable in isolation.