Does no one judge distance over the ground from altitude anymore?
I'm with Tinpis...look out the window. If you want to make it a semi- academic exercise. Cross the runway. Give it about 15-20 seconds and make the turn. If you're close to the runway, then either start your descent on downwind and plan for a continuous base turn onto final, or just aim a little wider on downwind to give yourself room. If you're too wide, then continue to the next aerodrome and call it a planned diversion. You'll get the hang of it.
In higher performance aircraft, that turn is a nice way to get rid of speed to get the gear out.