As the slugs had decimated my potatoes I decided to dig up a small section of the bed to see what was what. The first few to come up were smaller than an egg but as I dug a bit deeper a few good sized ones came up. Those two in my hand are just over 300g each. The total weight of this first batch was 1kg. Based on this I'm guessing I'll get around 10kg from the bed. Not a great result but I'm happy enough given my inattention to the slug problem.