At the log pile with a 10-inch salad bowl in mind
Tell it the finished bowl you're after and it hands back the blank to cut — diameter, wall, and height, rounded up to the quarter inch, with its assumptions stated in the answer. Everything stays in your browser.
The bowl
The numbers here are yours to check. This page does arithmetic on what you type — it cannot see your recipe, your equipment or your batch.
Want it to remember?
In MadeKeeper the blank comes out of your logged inventory at what the wood actually cost you, and the twice-turned pair — rough date to return date — rides along with your drying notes. See for woodturners or poke around the live demo. $19/mo for the whole back office, kept for as long as you stay. The shop stays free for cost a piece and one fair — no product cap. The tax packet, Etsy and Square, and more fairs are the $19.
Free woodturning calculator
The math here is the club's own folk math. It's worth knowing where each number comes from — and which ones you should change to match your wood.
Why does a 10-inch bowl call for an 11-inch blank?
Because green wood moves as it dries — a rough-out shrinks and goes oval, and how much depends on the species and how the blank rides the grain. That's a contested number, which is why it's a setting: the calculator defaults to a 10 percent ovaling allowance, finished diameter times 1.10, which is how 10 inches becomes 11. That default is a convention, not a fact about your tree. If your cherry has been coming back rounder than that, change the setting — your own species experience wins.
Where does the 1.1-inch rough wall come from?
That's the turning-club rule of thumb: leave the rough wall about a tenth of the diameter, so the bowl dries without a thin spot leading the way and still has meat left to true up round. The calculator divides the blank diameter by 10 by default — an 11-inch blank gets roughly a 1.1-inch wall. The divisor is a setting, because it's a rule of thumb, not physics — a well-behaved species can get away with a thinner wall, and a cranky one can't.
How tall does the blank for a 4-inch bowl need to be?
Finished height, plus a tenon for your chuck, plus the same rough-wall allowance under the bottom. With the defaults that's 4 inches of bowl, a half-inch tenon, and about 1.1 inches of bottom — call it 5.6 inches of blank before rounding. The tenon length is yours: half an inch is only the default, and the right number is whatever your chuck jaws actually want.
Why does everything round up to the quarter inch?
Because a blank cut small is firewood. Extra wood turns away in a few passes; missing wood ends the project at the bandsaw, so the calculator always rounds up — 5.6 inches of height becomes 5.75, never 5.5. The answer also states the ovaling percentage and wall rule it used, so you can check its assumptions against what your wood has actually been doing.