There are a number of common units in use in the media. Here's a guide:
Double-decker bus Used to measure height, or sometimes length. Why anyone should be able to envisage a stack of buses is a mystery.
Wales Used for the area of islands, icebergs and the size of asteroids.
Belgium See Wales. Used for larger areas (did you know that Belgium was larger than Wales?)
Isle of Wight See Wales. Very handy for asteroids in particular
Football pitches Used for smaller areas and sometimes length. Even stranger, sometimes height.
Wembley Stadium Sometimes filled with stuff ("enough rubbish to fill Wembley stadium several times over") or people ("ten Wembley stadiums full of people are affected")
I think it's time we moved to a new system that makes more sense to everyone, so here are my recommendations:
London Eye Used for height. Many people have seen it, and many have been up in it, so they know what it's like to look down from it. "Three times the height of the London Eye" makes real sense.
"Strictly" dance floor Used for areas, replacing football pitches. Far more people watch Strictly than sit in football stadiums these days.
Shopping Mall A replacement for Wembley stadium. OK, malls vary in size, but these comparisons are pretty vague at the best of times
Apple Store Used for volumes of stuff, replacing Olympic swimming pools. I rather like the idea of "enough PCs to fill an Apple Store"
Alas, as for really large areas, I'm stumped. Any ideas?