Ok, so I think that a business card size reference is a bad comparison. To give you a better example of the picture's measurement itself. If you see look at the picture horizontally and use your fingers to measure; the width of the picture is about four fingers and the height is about three fingers. Hope this helps!
I am using a cloth tape measure to measure the Polaroid pictures (including borders) and I also measured several business cards (which are a bit larger in both width and length) and credit/debit cards (which are almost the same size as the developed Polaroid). My original answer was just to give readers an approximate idea of how small they are compared to standard developed picture sizes. There is no doubt about it - the Polaroid 300 Instant pictures are small which may be a decision breaker in some instances.