Guitars with lower bout widths of 15 inches or less are in general based on classic designs and designations from Martin. Part II of this guide to acoustic guitar sizes looks at guitars with lower bouts greater than 15 inches wide. Things are not as clear cut here as with smaller guitars. The variety of distinctive shapes is larger than for small guitars and some designations, e.g., dreadnought, cannot be as reliably tied to the lower bout width when you start comparing guitars from different makers.

Dreadnought guitars.

Make	Size	Frets to body	Lower Bout	Depth	Body Length	Scale	Nut Width	Example	Size Name
Martin	D	12	15.625	4.75	20.9375	25.4	1.75	HD-28VS	Dreadnought
Martin	D	14	15.625	4.875	20	25.4	1.6875	D-28	Dreadnought
Taylor	#10	14	16	4.625	20	25.5	1.6875	210 DLX	Dreadnought
Gibson	Dove etc (square shoulder dreadnought)	14	16.25	?	?	?	?	Dove	Dreadnought

Dreadnought guitars have a distinctive shape with a wider waist, a deeper body and a lower bout of approximately 16 inches compared to most guitars. But as you can see from the table, the lower bout width varies slightly among the major guitar makes. Dreadnoughts with 12 frets to the body are rare now but the original dreadnought was a 12-fret instrument. A 12-fret dreadnought is going to have sloped shoulders. The shoulders became more squared when the switch was made to 14-frets at the neck joint.

The Gibson Dove is pictured on the right.

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Guitars as Big as a Dreadnought but Not Quite a Dreadnought.

Make	Size	Frets to body	Lower Bout	Depth	Body Length	Scale	Nut Width	Example	Size Name
Taylor	#14	14	16	4.625	20	25.5	1.6875	214ce	Grand Auditorium
Gibson	AJ	14	16	?	?	25.5	?		Advanced Jumbo
Gibson	J45	14	16	?	?	?	?	J45

Some of these guitars are 14-fret slope shouldered dreadnoughts and some are maybe something else (such as the 214ce from Taylor). They all have a 16 inch lower bout and aren’t the traditional 14-fret dreadnought with squared shoulders on the upper bout.

The Gibson Advanced Jumbo is shown on the left. One of Gibson’s most successful and popular acoustic guitars, the J-45, is shown on the right.

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Jumbos or Lower Bouts wider than 16 inches.

Make	Size	Frets to body	Lower Bout	Depth	Body Length	Scale	Nut Width	Example	Size Name
Taylor	#16	14	16.25	4.625	20	25.5	1.75	316	Grand Symphony
Taylor	#18	14	16.75	5	20.625	25.5	1.75	818e	Grand Orchestra
Gibson	SJ	14	17	4.75	?	?	?	SJ-200	Super Jumbo

The Gibson Jumbo (J or SJ, 100 or 200) is a big guitar. They are distinctively different fromdreadnoughts because they have a narrower waist. The SJ-200 has a 17 inch lower bout and Gibson likes to let you know it is nicknamed the King of the Flattop guitars. It was the guitar played Elvis.

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