How large is "1 large beef bouillon cube" for risotto?
I would check the recipe and see how much stock that requires, and then compare that to how much stock your bouillon cubes make. If it's close, you're probably fine. This assumes you make standard stock before using the cube, of course, and not concentrate. Does the recipe give any other clues? 

If you can't get any joy this way, I'd suggest you just guess, erring on the side of bland, and taste as you go.