You can estimate it pretty easily. In the side profile, the bucket approximates a triangle. The surface touching the ground can be considered the base, b. The verticle side at right angles to the base can be considered the height, h. The interior width, w, can be measured as can the interior values of b and h. So the volume, V, can be calculated as V=1/2(b*h*w). For example if b =1.5 ft, h= 1.5 ft and w= 6ft, V =6.75 cu ft or 0.25 cu yards.