Here’s my structure for answering this Google estimation interview question:

1 phone per person (Assumption)

Global Population = 8B

iPhone is associated mainly with three things:

1. It is expensive than regular android phone
2. It has a brand value and attracts brand conscious people who are willing to spend
3. Technically advanced but the boundaries are diminishing with each passing day

Since we are talking globally – Due to the above two factor I will segregate the consumers into three broad categories:

Developed countries (20%) = 1.6B

Developing Countries (40%) = 3.2B

Under developed countries (40%) = 3.2B

Smartphone penetration

Developed countries (90%) of 1.6B = 1.4B

Developing Countries (70%) of 3.2B = 2.2B

Under developed countries (40%) of 3.2B = 1.2B

The assumption is that iPhone and Android are the only major players and capture 100% of the TAM. In reality, there are a few more OS like KaiOS in India, and a few in Russia and China but these two are the predominant OS in the smartphone market. In the end, we may factor it down by some percentage to address the other players as well.

Android is the major player globally but its percentage share varies drastically amongst our segmented geographies.

Share of iPhone and Android