How much gold is there in the world?

Imagine if you were a super-villain who had taken control of all the world's gold, and had decided to melt it down to make a cube. How big would it be? Hundreds of metres cubed, thousands even?

Actually, it's unlikely to be anything like that size.

Warren Buffet, one of the world's richest investors, says the total amount of gold in the world - the gold above ground, that is - could fit into a cube with sides of just 20m (67ft).

But is that all there is? And if so, how do we know?

A figure that is widely used by investors comes from Thomson Reuters GFMS, which produces an annual gold survey.

Their latest figure for all the gold in the world is 171,300 tonnes - which is almost exactly the same as the amount in our super-villain's imaginary cube.

A cube made of 171,300 tonnes would be about 20.7m (68ft) on each side. Or to put it another way, it would reach to 9.8m above ground level if exactly covering Wimbledon Centre Court.

But not everyone agrees with the GFMS figures.

Estimates range from 155,244 tonnes, marginally less than the GFMS figure, to about 16 times that amount - 2.5 million tonnes.

That bigger figure would make a cube of sides 50m (166ft) long, or a column of gold towering 143m above Wimbledon centre court.

- BBC.co.uk