Segmented Bowl Ring & Cut List Calculator
Enter the finished base, rim, height, ring thickness, wall thickness, allowances, and kerf. The calculator turns that profile into a ring-by-ring cut list with long and short segment edges, strip widths, stock length, and estimated board feet.
Total stock length206.38
- Number of rings
- 8
- Planned stack height
- 6
- Miter setting
- 15
- Total segments
- 96
- Widest required strip
- 1
- Estimated lumber volume
- 1.07
Per-ring cut list
| Ring | Start elevation | End elevation | Rough OD | Rough ID | Long edge | Short edge | Strip width | Segments | Strip length |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 0 | 0.75 | 6.75 | 4.75 | 1.81 | 1.27 | 1 | 12 | 20.17 |
| 2 | 0.75 | 1.5 | 7.25 | 5.25 | 1.94 | 1.41 | 1 | 12 | 21.78 |
| 3 | 1.5 | 2.25 | 7.75 | 5.75 | 2.08 | 1.54 | 1 | 12 | 23.39 |
| 4 | 2.25 | 3 | 8.25 | 6.25 | 2.21 | 1.67 | 1 | 12 | 24.99 |
| 5 | 3 | 3.75 | 8.75 | 6.75 | 2.34 | 1.81 | 1 | 12 | 26.6 |
| 6 | 3.75 | 4.5 | 9.25 | 7.25 | 2.48 | 1.94 | 1 | 12 | 28.21 |
| 7 | 4.5 | 5.25 | 9.75 | 7.75 | 2.61 | 2.08 | 1 | 12 | 29.82 |
| 8 | 5.25 | 6 | 10.25 | 8.25 | 2.75 | 2.21 | 1 | 12 | 31.42 |
Uses alternating-angle strip cutting with a projected kerf of 0.129 in.
How to use this calculator
- Enter the finished outside diameters at the base and rim of the segmented section.
- Enter the finished stacked height, ring thickness, wall thickness, and number of segments per ring.
- Add outside and inside turning allowances that match your comfort with milling and turning accuracy.
- Enter the measured saw kerf and choose whether your strip is cut with alternating miters or one-direction cuts.
- Use the table to mill strip widths and cut each ring before checking the warnings in the notes.
How the cut list is calculated
This calculator models the outside of the segmented section as a straight line from the finished base diameter to the finished rim diameter. It divides the target height by the finished ring thickness and rounds up to a whole number of rings. If the height does not divide evenly, the planned stack is slightly taller than requested so every ring can use the same milled thickness.
For each ring, the calculator checks both the lower and upper edge of the layer. That matters for bowls that flare outward and for forms that narrow toward the rim. The larger boundary diameter sets the rough outside diameter after adding outside turning allowance. The smaller boundary diameter sets the rough inside opening after subtracting the finished wall thickness and inside turning allowance.
The segment lengths use the tangent construction for a regular polygon. Let n be the segment count per ring and theta = pi / n. The saw miter setting is 180 / n degrees. For one ring, Do is rough outside diameter and Di is rough inside diameter. The long edge is Lo = Do * tan(theta), the short edge is Li = Di * tan(theta), and the radial strip width is W = (Do - Di) / 2.
Kerf is projected along the strip because the blade crosses the stock at the miter angle: kp = kerf / cos(theta). With alternating cuts, the estimated strip length is n * (Lo + Li) / 2 + (n + 1) * kp. With one-direction cuts, it is n * Lo + (n + 1) * kp. The total stock length is the sum of all ring strip lengths, and board feet are summed as strip length * strip width * ring thickness / 144.
What moves the result most
Segment count changes both the miter setting and the segment edge length. More segments make each piece shorter but increase the number of cuts and the amount of kerf loss. Turning allowance and wall thickness change strip width directly, while a larger rim or base changes the outer long edge on the rings near that part of the form.
What this calculator leaves out
The model is a planning cut list, not a turning plan for a finished curve. It does not account for defects, color matching, end checking, test pieces, glue-up squeeze, sanding loss, jig setup waste, or segmented patterns that change species around a ring. Curved, beaded, or compound profiles should be broken into separate control diameters or drawn in dedicated design software.
Worked example
Suppose the finished segmented section is 6 in at the base, 10 in at the rim, and 6 in tall. With 0.75 in finished rings, 0.5 in wall thickness, 12 segments per ring, 0.125 in outside and inside turning allowances, a 0.125 in saw kerf, and alternating cuts, the calculator plans 8 rings and 96 total segments.
The miter setting is 180 / 12 = 15 degrees. On the first ring, the rough outside diameter is 6.75 in and the rough inside diameter is 4.75 in, so the long edge is about 1.809 in, the short edge is about 1.273 in, and the strip width is 1 in. The full default bowl uses about 206.38 in of kerf-adjusted strip length and about 1.075 board feet before extra shop waste.
Common questions
What angle should I cut for a 12-segment ring?
Set the saw miter to 15 degrees for a 12-segment ring. The included angle at each joint is 30 degrees, and each segment supplies half of that angle.
Why is segment length based on the tangent instead of circumference?
A ring made from straight segments is a regular polygon, not a true circle. The segment edge is the side of a polygon tangent to the turning diameter, so the practical cut length comes from diameter times the tangent of pi divided by the segment count.
Should I measure the long edge or the short edge?
For an open ring, the outside face is the long edge and the inside face is the short edge. The table gives both because strip-cutting methods and stop-block setups differ, and because one-direction cutting often needs stock based on the long edge.
How do alternating miter cuts reduce waste?
Alternating cuts flip the miter direction from piece to piece, so neighboring cuts share the taper instead of repeatedly trimming back to the long edge. The calculator estimates that layout with the average of the long and short edges plus projected kerf.
Can this plan a bowl that narrows toward the rim?
Yes. Each ring is evaluated at both its lower and upper boundary, so the larger boundary controls the rough outside diameter and the smaller boundary controls the rough inside opening. That keeps the math valid for either a flared or narrowing straight profile.
Why is the planned stack taller than my requested height?
Ring count has to be a whole number. When the requested height is not an exact multiple of ring thickness, the calculator rounds up and reports the extra stack height so you can turn, sand, or trim it deliberately.