depends on scale and what it is. Civil war, big scale, enough for a backing...
small, Civil war shirting, fat qtr or up to 1 yd.
Novelty, fat qtr or up to 1 yd
panel~ 1 to 2
Mostly if it is a "timeless" type , like Civil War or reproduction, which will ALWAYS be around and in style, and I love it, I buy lots.
If it is a flash in the pan, less is more...