8 1/4" X 2 1/4". Fine grit (25 micron) goldtone diamond surface on one side, Black ceramic stone on the other side. DC521 is a bench stone of a less common category, since it offers two different kinds of stones. The Yellow part is a fast and aggressive diamond stone, while the dark is a slow, very fine ceramic stone. Both surfaces are precision flat, which is a prerequisite for perfect sharpening results. The diamond stone works fast and should be used if the edge is very thick. The sharpness obtained is usually enough for everyday tasks. The ceramic whetstone works much more slowly and gives a smoother, razor-sharp edge when necessary. For tools and chef knives, this bench stone is among the best Offered.