How to estimate the number of Taxis outside Delhi Airport ?

First: You MUST clarify if it's at a certain time of day/night. i.e. noon, midnight, etc. Is this at any given point in time?

Top-Down

Population of Delhi/Surrounding areas residents...subset of which would be flying in/out

PLUS population of daily visitors (business / tourist)

% of each group that would need taxis

Multiply out

 Divide by time period unit 

Bottom-up

When you've been to a large airport, how many landings have you see on the board at one time?

How many per hour?

How many peak hours per day?

How many non-peak hours per day and what % of peak would this be?

 # of people in an average plane (i.e. landing)

Multiply out

 Divide by time period unit 

Is Delhi Airport probably larger or smaller than this sample airport (multiply by that factor)

Hello!

Have a look at this free case I did for the PrepL library, that is precisely about flights stimation in an airport.

From there it´s easy to extrapolate any "fleet" estimation I hope.

https://www.preplounge.com/en/management-consulting-cases/candidate-led-usual-style/intermediate/covid-19-impact-on-heathrow-airport-197

Hope you find it useful!