How fast is the expansion of space?When you take any object that’s detectable through the science of astronomy, you’re always measuring some form of energy — usually light — that’s either emitted or absorbed by the object in question.

We know that the expanding Universe causes redshifts; we know how two objects moving away from one another causes a redshift. If you want to translate the expansion of the Universe into a speed, that’s what you have to do: ask yourself, “Based on the redshift that I’m measuring due to the fact that space is expanding, how fast, in terms of a relative recession speed between the source and the observer, would things need to be moving to give the same value for a redshift

In reality, these objects aren’t moving through the Universe at that speed at all, but rather the space between bound objects is expanding. It still doesn’t give a definitive answer as we can only perceive the observable universe.