The basic shape of acoustic guitars has not changed , from the Standard flat top , the Dreadnought or flat top to the Classical. The characteristic figure of eight featuring the upper bout, the waist and the lower bout, but the relative dimensions often vary.
The smaller upper bout enhances the upper or treble frequencies while the larger bout enhances the bass or bottom frequencies . Try dropping a coin through the sound hole into the sound box of the guitar and try shaking the instrument so it rattles around, moving from bout to bout to demonstrate the sound difference.
The overall size of guitars varies from one type to another, Flat top steel string acoustic range from the “standard” size up to the larger “jumbo” size and back to the “ Dreadnought “ shape.
The Standard acoustic instrument is very similar to the Classical guitar in many ways in both shape and size. The Standard Flat top is 102cm overall, 37cm at the widest and 12 cm deep, while the Jumbo is 103.5cm overall, 41cm wide and 12.5 deep, the Classical being 98cm overall, 37cm at the widest and 10cm deep. Happy Playing .