Clay Volume Calculator

Sculptors rarely fill their full bounding box with material — an arm, a torso, or an abstract form typically occupies well under half of the rectangular box that contains it — so this calculator applies a fixed 38% fill factor to your entered height, width, and depth to estimate the sculpture's actual volume, rather than just multiplying the three dimensions straight through. For hollow (coil- or slab-built) pieces, it then carves out an interior cavity: it shrinks each dimension by twice your wall thickness (since the wall comes off both sides), applies that same 38% fill factor to the resulting interior box, and subtracts it from the solid volume — an approximation, since real hollow forms aren't simply smaller copies of the outer shape, but a reasonable estimate for planning purchases. Weight is volume times the wet density for your chosen clay body (earthenware, stoneware, porcelain, or oil-based non-firing clay like Chavant), and the calculator tacks on a flat 12% waste allowance for trimming, wedging loss, and reworking before converting the total to standard 25-lb and 50-lb bag counts.

Firing shrinkage — the linear percentage each clay type loses as it dries and vitrifies in the kiln (roughly 8% for earthenware up to 12% for porcelain, zero for oil-based clay that never fires) — is applied to the entered height and width so you can see the piece's actual finished size, not just its greenware dimensions. A common mixup: shrinkage is compounding and three-dimensional, so a 10% linear shrinkage means the piece loses nearly 27% of its volume, not 10%.