I caught a bit of a BBC programme earlier where they were doing the string test. I've never heard of it before, but it makes perfect sense. If your waist measurement is more than half your height, you are overweight. And because it's around your waist, it indicates how much visceral fat you have. That's the really bad type.
So, you get a piece of string, cut it to the length of your height (heel to head), fold it in half and put it around your waist. If it doesn't meet, you're overweight. Very simple.
I know that BMI is controversial, but with this, you can't really argue against it, can you? Unless you're pregnant!