Rough-Out Wall Thickness & Drying Time Calculator
For the classic "twice-turning" method: rough-turn a green blank thick, let it dry and distort, then true it up into the finished bowl. Pick your target bowl diameter and species for a starting wall thickness and a drying-time range.
Rough-out guidance
1in rough wall
Starting point: 10% of bowl diameter (a widely-used shop rule, not a guarantee), floored at 0.5in for small blanks.
Typical drying time (paper-bag method): 4–7 months
Black Walnut has a comparatively low warp spread (~2.3 percentage points) in this reference — it tends to stay rounder than most as it dries, so a slightly thinner rough wall is often workable.
The reliable way to know it's actually dry: weigh the blank weekly on a kitchen scale. Once the weight stops dropping between weighings, it's ready for final turning — trust the scale over the calendar.
Need blank sizes first? Use the log to bowl blank calculator, or check species properties on the turning wood reference chart.
Frequently asked questions
- Why 10% of the diameter for the rough wall?
- It's a widely-repeated shop rule among turners (see the American Association of Woodturners' own forum discussion on twice-turned wall thickness): a 10-inch bowl gets roughly a 1-inch rough wall. It leaves enough material to true up the bowl into a round shape again after it distorts (ovals) while drying. It's a starting point, not a formula derived from wood science — some turners go thinner on stable species and thicker on ones known to move a lot.
- Why does the drying-time range change with wall thickness, not species?
- Every source this tool is built from ties drying time to how much wood the moisture has to travel through, not to species — a thicker rough wall simply takes longer to reach a stable moisture content. Species does still affect how much the blank ovals while drying (see the warp-spread note below the result and the reference chart), which is why it changes the recommended wall-thickness starting point — but the reported 3-8 month drying range here scales with wall thickness only. Every source agrees the reliable signal is weight stabilizing on a scale, not a calendar date.
- What is the paper-bag method?
- After rough-turning, the wet blank (often with a handful of its own wet shavings) goes into a paper grocery bag, stored somewhere cool, dark, and free of airflow. The bag slows moisture loss so the wood has time to relax rather than crack. Turners typically re-bag it in a fresh bag every week or two and weigh it each time.
- Is my data uploaded anywhere?
- No. Everything runs in your browser — nothing you type is sent to a server.