It's impossible to give a meaningful answer to "how many" of anything it would take to fill up Venus without knowing what we are trying to fill it with.

Here's why:

* Venus is a planet: Planets are giant celestial bodies.

* We don't fill planets: We don't fill planets with things the way we might fill a container.

To answer your question, we need more information. For example:

* What are we trying to fill Venus with? Water? Rocks? Air?

* What is the desired outcome? Are we trying to create a habitable atmosphere? Are we trying to change the planet's mass?

Once we have this information, we can start to think about the volume of Venus and the volume of whatever we are trying to fill it with.

Let me know if you have a more specific question!