[ThrowawayR2]

The only mention I've been able to find online suggest that only about 1/3 of Google's workforce are in R&D: https://www.quora.com/What-percentage-of-Google-employees-ar...

"This information is most likely buried in Google’s annual report — the last one I could dig up is their 2015 fiscal year end report. According to the paper published by Google Inc and Alphabet Inc, there are 61,814 full-time employees with 23,336 in research and development."

Bear in mind R&D isn't pure developers. It also includes QA and project/program management roles.

[qeqeqeqe]

That source you cite literally says that "45% of Google employees are programmers."

[ThrowawayR2]

He cites numbers from Google's previous financial reports (likely to be valid) and then adds a guess of 45% at the end (less likely to be valid). If you want to believe the guess, well, that's up to you.