Sizing America's EV charging infrastructure: public sites, ports and home chargers
Company: Google
Role: Product Manager
Category: Product / Decision Making
Difficulty: medium
Interview Round: Other
Estimate how many electric vehicle charging stations there are in the United States today. Explain what you are counting, the approach you choose, the assumptions behind each step, and how you would check that your final number is reasonable.
```hint Settle the unit before the math
"Charging station" can mean a public location with several plugs, a single plug, or a charger in someone's garage, and these counts differ by an order of magnitude or more. Agree on the unit first, then anchor the estimate on a quantity you can size with confidence and work from it toward chargers.
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### Clarifying Questions
- Does a "station" mean a charging location, the way a gas station is one location with many pumps, or each individual charging port?
- Should the count include only chargers open to the public, or also private ones in home garages, at workplaces and in fleet depots?
- Which vehicles are in scope: passenger cars only, or also buses, delivery trucks, e-bikes and scooters? Does battery swapping count?
- Does charging from an ordinary wall outlet, with no dedicated charging unit, count as a charger?
### What a Strong Answer Covers
- A clear definition of the counting unit (sites versus ports, public versus private) and why the choice changes the answer.
- An equation that ties the charger count to something estimable, such as the size of the EV fleet and how much of its charging happens in public, or the places that host chargers.
- Round, explicitly labeled assumptions and arithmetic that is easy to follow, with consistent units.
- At least one independent cross-check or sanity check, and a view of which assumptions the result is most sensitive to.
- A final number with a sensible range, and a note on how private chargers would change it.
### Follow-up Questions
- The interviewer now says chargers in private homes count too. How does your estimate change, and which new assumptions matter most?
- How would you estimate how many more fast-charging ports the country would need if EVs became a much larger share of the cars on the road?
- Your estimate turns out to be three times the published count. How would you work out which assumption was wrong?
Overview: A product manager estimation question asking for the number of electric vehicle charging stations in the United States. It tests defining the counting unit (public sites, ports or home chargers), building a clear equation from the EV fleet or host locations, labeling assumptions, and sanity-checking the result.