I'm trying to put a spreadsheet together that shows the co-moving volume of the universe from the time soon after the Big Bang through the present and then as predicted into the future. I am pretty sure that all I have to do is use the scale factor $a(t)$ as derived from the FLRW equations (I suppose this is what the scale factor is for anyway). How is the scale factor meant to be used with the volume if I want to calculate $V(t)$?
1 - Is it , $V(t) = V_0 a(t)^3 $?
2 - Is it simply, $V(t) = V_0 a(t)$?
3 - Or $R(t) = a(t) R_0 $ and then find $V(t)$ from $R(t)$?