Originally Posted by David Lyga
We all know that because of the need for movie film to withstand the rigors of constant, steady movement along a projector's sprockets (without tearing!) that this film had to have large sprocket holes in order to be ‘born’. That factor took up a lot of real estate and that waste is part of the legacy that movie film has left for the ‘identical’ still film. But do we know what the quantified result is? Absolutely shocking! We are required to waste about half of this expensive film just because of that ‘necessity’.

Counting the leader, a 36 exposure roll of film is about 63 inches in length. With avoirdupois translated into metric, that 63 inches becomes 1600 millimeters per roll. (i.e. 63 inches x 25.4mm per inch). This 1600mm length times the 35mm width becomes 56,000 square millimeters of film per roll, total. Now, we take 36 pictures on the roll and each frame is 24mm x 36mm, yielding 864 square millimeters per frame or 31,104mm (I.e. 864 x 36 frames) used for actual image recording. 31,104 divided by 56,000 is only about 55.5% of the total film area that is actually used! We waste almost half.

Again, even worse: Counting the leader, a 24 exposure roll of film is about 45 inches in length. With avoirdupois translated into metric, that 45 inches becomes 1143 millimeters per roll. (i.e. 45 inches x 25.4mm per inch). This 1143mm length times the 35mm width becomes 40,005 square millimeters of film per roll, total. Now, we take 24 pictures on the roll and each frame is 24mm x 36mm, yielding 864 square millimeters per frame or 20,736mm (I.e. 864 x 24 frames) used for actual image recording. 20,736 divided by 40,005 is only about 52% of the total film area that is actually used! Again we waste almost half.

What more is there to say about the most popular film size ever created? 120 film does not waste nearly as much and sheet film wastes virtually none. And, remember, my calculations assume that all frames are usable. – David Lyga
If you think of those "unused" areas as supports or carriers for the negative, there is no waste. How else would you put the slide in a mount, or negative in a carrier without encroaching on the image?