Questions to those that monitor the weight of their hive.
When/if your hive swarms what weight drop do you see?
What hive configuration is the weight drop associated with? (i.e. how many brood boxes and how many supers? What size boxes (full depth langstroth? National? Etc)
What time of season is this associated with? (Early, mid, late)
Thanks in advance!
Swarms can vary greatly in size. I’d say typically you lose about 3 pounds of bees but it could be much higher or much lower. Those bees probably can’t carry more than their weight in honey. So an average swarm maybe between 3 and 6 pounds?
Fortunately, my Arnia monitored hive has never swarmed. 
I think Arnia have some swarm example weight graphs on their web site though. 
I’ve not had my hives swarm with a scale on them.
A friend has some swarm traps with scales, over kill?
He has caught swarms weighing between 1.3 - 5kg.
A swarm I thought was determined by the size of the originating hive. If each super has ~20,000 bees a two super hive could issue 50% of the bees. Each bee weighs ~0.1g, I’m not sure what extra weight the honey makes but it would be hard to account for given the resolution of the scales we use. But 2kg would be roughly the swarm size.
I reckon @Michael_Bush is right that our average swarms are around 3lb from managed hives:
3lb is ~1.3kg
11lb is ~5kg
Wait until you get an orientation flight that is larger than that and you are at work…
Adam
