Estimation question

How many mobile phones are there in the world?

Practice this question out loud. An AI interviewer asks it, follows up like a real interviewer would, and scores your answer. Type or speak.

What this question tests

Tests basic structured estimation anchored on global population and device-ownership assumptions.

State the goal: estimate the total number of mobile phones in use worldwide.
Anchor on global population: assume roughly 8 billion people worldwide.
Estimate mobile phone penetration: assume about 70% of the population owns at least one active mobile phone, accounting for young children and areas with low connectivity.
Compute base ownership: 8 billion times 70%, about 5.6 billion people owning a phone.
Adjust for multiple-device owners: assume 10-15% of owners have a second active device (work and personal), adding roughly 700 million more devices.
Compute total: roughly 6.3 billion active mobile phones, then sanity-check against known global mobile subscription statistics.

Anchors on a known, defensible figure, global population, before layering penetration and multi-device assumptions.
States penetration and multi-device ownership as separate, explicit assumptions rather than one blended guess.
Accounts for a realistic non-owner population, children and low-connectivity regions, instead of assuming near-100% ownership.
Sanity-checks the final figure against publicly known mobile subscription statistics.

Assuming nearly 1:1 phone ownership with global population, ignoring children and connectivity gaps.
Ignoring multi-device ownership, undercounting total phones in circulation.

How would you adjust this estimate for smartphones specifically versus basic phones?
Which region would contribute the most to this total, and why?