I figure a five gallon bucket normally filled (a few inches below the top) as basically a half bushel, If one is doing quick figuring, but the normal way is by weighing it today,

a volume bushel is 1 and 1/4 cubit foot by volume, but the volume method is not normally used in to days commerce, unless your measuring a bin or granary or pile and trying to get an estimate of the volume that is there, and then normally there are weight factors that goes into the final calculation of the bushels that are estimated there to sell or work with.