Green Wood Shrinkage Calculator

Wood doesn't shrink the same amount in every direction, and that mismatch is exactly why a bowl turned perfectly round from green wood ends up oval once it dries. This calculator uses species-specific tangential and radial shrinkage percentages published in the USDA Forest Products Laboratory's Wood Handbook (or your own custom values) — tangential shrinkage runs across the growth rings and is always larger, radial shrinkage runs along the rings and is smaller — and scales each down proportionally to how far your target moisture content actually falls below the green starting point, relative to the 30% fiber saturation point where dimensional shrinkage begins (wood loses free water above that point with no shrinkage at all, so if your green wood is already near or below 30% MC, the calculation adjusts to reflect less shrinkage still ahead of it). Note that whenever Green MC is at or above 30%, only that at-or-above fact matters — entering 40% versus 150% produces the identical result, since the calculation always starts counting shrinkage from the 30% fiber saturation point in that range rather than from your exact green reading. The result: the diameter shrinks more along the tangential (short) axis than the radial (long) axis, producing the oval "ovality" figure, while depth — which the calculator treats as shrinking radially — and wall thickness change by their respective directional rates too.

A wall that was a uniform 1/2 inch when turned green won't stay uniform; it thins more on the tangential faces than the radial ones. The practical takeaway is the recommended rough-turned wall thickness, set at the larger of 1 inch or 10% of diameter, which gives you enough material margin to true up an oval rim and re-turn a clean round wall after the piece has finished drying and moving. This is the core logic behind "twice-turned" bowl technique.