Fermi Estimate: Total Bricks in New York's Building Stock

In a product manager interview, you are asked to estimate the number of bricks in New York. You have no access to data, so build the estimate from quantities you can reason about, state each assumption as you make it, and finish with a number. ```hint Find a countable unit Bricks themselves are impossible to count, but the things they are built into are not. Pick a unit you can estimate from population, then work out how much brick one such unit contains. ``` ### Clarifying Questions - Does "New York" mean New York City's five boroughs or the whole state? - Which bricks count: only those in standing buildings, or also sidewalks, paving, garden walls and bricks sitting in supply yards? - For a wall that is several bricks thick, should every brick in its thickness count, or only the visible face? - Is an order-of-magnitude answer enough, or should the estimate come with a range? ### What a Strong Answer Covers - Scope settled up front: the geographic area and which bricks are in and out. - An equation that splits the total into factors you can estimate separately, such as building counts by type, the share built of brick, wall area per building and bricks per square foot of wall. - Round, labeled assumptions with consistent units, and arithmetic that can be followed step by step. - At least one sanity check from a different angle, and a note on which assumptions move the answer most. ### Follow-up Questions - Which single assumption has the biggest effect on your number, and how would you narrow it with an hour of research? - How would you check the result from the supply side, using how many bricks would have had to be produced over the city's history? - How would your approach change if the answer had to cover all of New York State?