I think it's pretty clear that an entire human brain is not required for the operation of consciousness. Certain people have lost massive portions of their brain and still maintained regular consciousness functioning. On top of that, the typical human brain only consumes about 20 watts of power to do its thing. So that's just a safe upper bound for the power required.
Over the last decade we've seen the rise of ML systems that have replicated or surpassed capabilities long thought to be the exclusive domain of the human brain. Think facial recognition, AlphaGo or the very recent DALL-E 2.
This had led me to the personal belief that we (in aggregate) likely already have the computing power to achieve not only artificial consciousness, but also AGI and beyond. We simply haven't figured out the correct model connectivity and parameters.