I never remember that conversion. I just remember that 1lb = 454 grams (as seen on the side of a pot of jam) and go from there. I wonder whether the TSA people have any idea what a gram is?

My last flight taking off from the US I had the remains of a large tube of toothpaste. They saw it and let it through. It's the inconsistency that worries me more than the silly rules. I don't think they're worried about most of this stuff getting on planes - they're just trying to show the public that they're on top of the situation. It's all PR.