If you train all 3 lifts equally, you should app squat and dl 1.5 times more then you bench.
But like urban said, most people dl more then they squat. although the numbers seem to catch up as you progress. think it has something to do with the fact that squatting requires squatting your own bw + the bar, as dl only involves lifting the bar.
This is just a rough estimate though. but it can be useful as reference. For instance:
if you bench more then you squat (like me:redface: ) then you know you neglected squating.