Matthew Longo and Patrick Haggard of University College London asked volunteers to point to the tips and bases of the fingers of one hand while it was hidden beneath a board. The researchers used an overhead camera to record the guessed positions, then compared these with the dimensions of the real hand.
On average, volunteers estimated that their hands were two-thirds wider than in reality, and their fingers a third shorter (Proceedings of the National Academy of Sciences, abstract
Unfortunately, the abstract doesn't describe the number of people studied, or who was included.
Is this a cross-cultural pattern? Do people with unusually good dexterity have better than average representation of the size of their hands?