Estimating an Exchange's Daily Traded Volume

"Estimate the total dollar volume traded on the NYSE in a single day." No calculator, no internet — just what you can reason your way to from numbers a market-facing candidate ought to have some feel for. The trap is trying to recall the actual figure rather than deriving it; the point of the question is to watch you build a chain of reasonable multiplications, not to test your memory of a statistic.

The decomposition

Daily dollar volume on an exchange is well approximated as:

$$\text{daily volume} \approx \text{total listed market cap} \times \text{daily turnover rate} .$$

In plain English: turnover rate is the fraction of a company's total market value that changes hands in a single day, and multiplying it by the total value of everything listed gives the dollar amount actually traded. Total listed market cap is a number worth anchoring: the entire US stock market is roughly $50 trillion, and the NYSE carries a large share of that, so call it $25–30 trillion. Daily turnover rate is trickier to guess cold, but a useful anchor is that annual turnover for US equities runs somewhere around 100–150% of market cap (i.e., the "average" dollar of market cap trades hands about once a year, sometimes more) — dividing by roughly 250 trading days a year gives a daily turnover rate around 0.4–0.6%.

Worked example

Using $27 trillion for NYSE-listed market cap and 0.5% daily turnover: $27 \times 0.005 = 0.135$, i.e. $135 billion per day. That's in the right ballpark — real NYSE daily dollar volume typically runs in the $150–250 billion range depending on volatility, so a Fermi chain built from two anchor numbers gets within a factor of ~1.5–2× of the actual figure, which is a strong result for this kind of estimate produced with no lookups.

A cross-check from a different angle

As a second, independent chain: the NYSE lists roughly 2,400 companies; if the average daily dollar volume per listed company is, say, $60 million (a mix of a few mega-cap names trading billions and many smaller names trading a few million), that gives $2{,}400 \times 60 \approx 144{,}000$, i.e. roughly $144 billion — landing close to the $135 billion from the turnover-rate chain. Two structurally different chains agreeing within ~10% is a strong signal neither one has a badly wrong assumption buried in it.