What is a real world application of Euler's formula?

Eulers can be used whenever ur bulding something n u need 2 know how the edges r going 2 be or wats the verticles n how many faces it has then ull be able 2 use it 2 help u figure it out n also if ur walking down the streets n ur wondering how many eges r there in the stairwall then ull know quiet easly!