A set of ceramic samples based on silicon carbide with substantially varying integral porosity (from 1 to 10 %) was studied. The pore size distribution was examined by optical microscopy (for pores ranging from 10 mm to hundreds of microns in size), scanning electron microscopy (0.5 - 10 mm), and small-angle X-ray scattering (0.04 - 0.20 mm). The obtained pore size distribution function was used to estimate the integral porosity of ceramics, which was compared with the estimates of porosity obtained by the dilatometric technique. Relative contributions of large, small, and fine pores into the integral porosity of ceramics were found. The average pore sizes and average distances between them were estimated for each range of pore sizes.