Sulfur hexaflouride?

Question

How dense is sulfur hexaflouride compared to water?

Answer 1

I suppose you aren't considering its gaseous state and for the water, you are only using its liquid state.  As a liquid, it is 1.329 Kg/L, which would be 1.329 times the density of liquid water.

It's solid density is 2510 kg/m^3.  That would be 2.51 times the density of water.