Here are the actual Dimensions for the iPods (in inches)...
iPod Shuffle - 3.3 x .98 x .33
iPod Mini - 3.6 x 2.0 x .5
iPod/iPod U2 - 4.1 x 2.4 x .57
iPod Photo - 4.1 x 2.4 x .63 or 4.1 x 2.4 x .75 (there are two versions)
Divide each dimension buy 48 or 35 to get the scaled size - OR- you can just eyeball it and make your standard iPod roughly the size of the palm on your figure's hand.