Estimation question

How many dollar bills are in circulation in the US?

Practice this question out loud. An AI interviewer asks it, follows up like a real interviewer would, and scores your answer. Type or speak.

What this question tests

Tests structured Fermi estimation using per-capita cash-holding assumptions rather than trying to recall a real statistic.

Frame it as US population times an estimated number of bills held per person, across wallets, registers and hoarded cash.
Assume a US population of roughly 330 million.
Assume the average person carries or holds around 10 to 15 physical bills at a time across denominations, say 12 as a working assumption.
Add a multiplier for cash sitting outside individual wallets, in business tills, ATMs and hoarded savings, roughly doubling the per-person figure to around 24.
Multiply: 330 million times about 24 bills gives roughly 8 billion bills in circulation, stated clearly as an assumption-based estimate.

States every assumption explicitly, average bills held and the business-cash multiplier, rather than presenting a guess as fact.
Separates personal cash from business and hoarded cash as two distinct pools, which meaningfully changes the estimate.
Shows the multiplication clearly so an interviewer can follow and challenge any step.

Guessing a round number with no shown reasoning or stated assumptions.
Ignoring that a large share of cash sits outside individual wallets in tills, vaults and hoarding.

How would this estimate change if you accounted for denomination mix, more $1 bills than $100 bills?
How would you sanity-check this against a number you might recall, like total currency value in circulation?