How many airports are in the US and in the World?

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How many airports are in the US and in the World?

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H P · Answer 1 · 2020-02-11T11:39:22+0000

Google estimation questions like these are a big part of a PM interview. Here's an idea of how you can approach it.

For this question, I am assuming that the ask is to get the commercial airports that are operational for domestic and international flights only.

Airports in the US

Total number of airports in the US = Avg # of commercial airports in each state * number of states

US being developed economy, a lot of travel happens over the air and it's air traffic is quite huge compared to the other countries.

There are 50 states in the US

Each state capital on an average has two airports
Each state on an average would have another 40 airports (domestic and international)

So we arrive at the number of = 50* 2+ 50*40 = 2100 commercial airports

Airports in the world

Total # of airports in the world = # of airports in developed countries+ # of airports in developing countries+ # of airports in under-developed countries

Total population in the world ~ 7 billion

Roughly 20% of them stay in developed economies, 50% in developing and 30% in under-developed

So we have 1.4 billion, 3.5 billion and 2.1 billion respectively

We use the US airport data as baseline for advanced economies and project it further

So for 400 million population (US population) we have 2100 airports

So for 1 billion population in advanced nations, we have ~5000 airports

So for 1.4 billion, we have ~5400 airports

For developing economies, we would assume a factor of 0.75 compared to developed nations

So we have ~3750 airports for every billion people

So for 3.5, we have ~13000 airports

For under-developed nations, we would assume a factor of 0.5

So we have 2500 airport for every billion people

So for 2.1, we have ~5000 airports

So total airport (commercial) in the world = 5400+13000+5000 = 23400

Stanislav Fedoseev · Answer 2 · 2020-03-18T17:25:35+0000

Part 1 - the US

I will assume that we only have to calculate the number of commercial airports, and not military/private.

For the US as a developed country I will assume that every city with a population above 50 000 people will have an airport. Very large cities, say above 10 mln, might have several, but their impact on a total number will be insignificant, therefore we can discard them.

Now we just have to calculate the number of cities with 50 000 residents or above.

1. Total US population - 300 mln

2. Country vs city dwellers distribution - 20% vs 80%. So a total of 240 mln people leave in cities

3. Lets assume that 30% of the city dwellers live in cities with less than 50 000 residents. That leaves us 70% - 168 mln people living in cities with airports to work with.

4. Finally, lets assume an average city population of 100 000 people for cities above 500 000 residents. That means that there are (168 000 000 / 100 000) cities with airports in the US = 1680 airports total

Part 2 - the world

For this, we will have to segment world population into 3 groups - developed countries, developing countries, undeveloped countries.

I will assume that the population size threshold for a city to have an airport increases as the size of economy per capita dicreases, as an airport is a large infrastractural investment.

1. Developed countries 1.5B out of total 7B Earth population - similar to US in distributions, avg. city size, will use the same formula. (1 500 mln*0.8*0.7)/100 000 = 8400 airports

2. Developing countries 3.5B out of 7B - 75% city dwellers, threshold for airport 150 000 people or more living in the city, only 50% live in cities above 150 000 residents, avg. city size in this group is 250 000. (2 500 mln*0,75*0,5)/250 000 = 5250 airports

3. Undeveloped countries 2B out of 7B - 60% city dwellers, threshold for airport 300 000 people or more living in the city, only 40% of city dwellers live in cities above 300 000 residents, avg. city size in this group is 500 000 (2 000 mln * 0,6 * 0,4)/500 000 = 960 airports

Total number of airports in the world is 8400 + 5250 + 960 = 14 610