Segmented Bowl Calculator & Ring Cut Planner

Shape a finished bowl profile and plan each horizontal ring, turning allowances and separate-segment wood strips.

Your ring plan

5 rings · 60 segments

3.75 in finished ring stack · 15° miter from square · 0.81 board ft of rectangular stock

Drag the profile below, then inspect rings or export a cut list.

Ring construction

MeasurementsThe physical plan stays the same.Segments in every ringWhole number, 3–96. Closed rings with no gaps.

Finished ring height · inThe final band may be shorter.Outside turning allowance · inExtra radius beyond the finished outside.Inside turning allowance · inExtra wood inside the finished hollow surface.Sanding allowance per ring · inAdded to each finished height for stock thickness.Saw kerf · inActual width removed perpendicular to the cut.Total end trim per strip · inExtra material at both strip ends combined.

Separate solid base blank

Optional measured square blank. The profile starts above this base; base construction and grain compatibility must be chosen separately.

Include a measured base blank

Profile coordinates

Finished profile

Enter finished outside and inside diameters at each height, measured from the bottom of the ring stack. Straight lines connect the stations. Curves need enough stations to describe them.

Station 1

Height above ring stack bottom · inThe first station stays at zero.Finished outside diameter · inThe maximum finished circle at this height.Finished inside diameter · inSmaller than the outside; 0 means no opening.

Station 2

Height above ring stack bottom · inKeep above the preceding station.Finished outside diameter · inThe maximum finished circle at this height.Finished inside diameter · inSmaller than the outside; 0 means no opening.

Station 3

Station 4

Station 5

Station 6

Up to 16 stations and 100 rings. Keep heights in ascending order and the inside diameter smaller than the outside.

Your turning envelope

Drag a profile point, or use its numeric fields. Focus a point and use arrow keys: left/right changes its diameter, up/down changes its height. Shift uses a smaller step.

Shaded bands show material available at every angle around the ring. The plan view below shows the full polygonal blank. Height begins above any separate base.

Guaranteed materialFinished surface

Ring to inspectSelect a shaded band or a row in the cut list.

Ring 1: dashed circles show the largest finished outside (5 in) and smallest finished opening (2.5 in) in this entire band. Solid polygons include the turning allowances.

Separate-segment cut method

Long edges stay on the same side. Discard triangular offcuts; reserve the projected saw kerf in each cell. This conservative method is not an optimized flip-cut layout.

Selected ring: 1
Long / short edge: 1.382 in / 0.606 in
Required usable strip width: 1.447 in
Stock thickness: 0.789 in
Total strip length: 19.035 in
Projected kerf per cell: 0.122 in

Complete ring cut list

Finished ring stack height: 3.75 in
Stock ring thicknesses combined: 3.947 in
Strip lengths combined: 127.328 in
Rectangular stock, including base: 0.81 board ft
Miter setting from square: 15°
Included segment angle: 30°

Ring heights below are finished heights. Stock thickness includes your per-ring sanding allowance. Strip lengths include kerf and total end trim; buy actual usable widths and thicknesses.

Height band	Finished height	Stock thickness	Segments	Long edge	Short edge	Stock width	Strip length
0 in–0.75 in	0.75 in	0.789 in	12	1.382 in	0.606 in	1.447 in	19.035 in
0.75 in–1.5 in	0.75 in	0.789 in	12	1.784 in	0.995 in	1.473 in	23.858 in
1.5 in–2.25 in	0.75 in	0.789 in	12	2.052 in	1.383 in	1.249 in	27.073 in
2.25 in–3 in	0.75 in	0.789 in	12	2.186 in	1.642 in	1.016 in	28.681 in
3 in–3.75 in	0.75 in	0.789 in	12	2.186 in	1.771 in	0.774 in	28.681 in

No separate base blank included.

Miter is measured from a square cut. A test ring and actual saw setup are still required. This tool does not certify glue joints, wood movement, lathe clearance or safe machining.

Kalkmi segmented bowl plan — measurements in in
5 rings; 12 segments each; miter 15° from square; included angle 30°
Finished ring-stack height: 3.75 in
Outside radius allowance: 0.079 in
Inside radius allowance: 0.079 in
Sanding thickness per ring: 0.039 in
Perpendicular saw kerf: 0.118 in
Total end trim per strip: 0.984 in
Separate segments, long edges on same side, triangular offcuts discarded; not optimized flip-cut nesting.
Finished profile stations (height, outside diameter, inside diameter):
1: 0 in | 3.5 in | 2.5 in
2: 0.75 in | 5 in | 4 in
3: 1.5 in | 6.5 in | 5.5 in
4: 2.25 in | 7.5 in | 6.5 in
5: 3 in | 8 in | 7 in
6: 3.75 in | 8 in | 7 in
Complete ring cuts:

Ring 1 — height band 0 in–0.75 in
  Finished height 0.75 in; stock thickness 0.789 in
  12 segments: long edge 1.382 in; short edge 0.606 in
  Strip width 1.447 in; strip length 19.035 in
  Finished outside envelope diameter 5 in; inside envelope diameter 2.5 in

Ring 2 — height band 0.75 in–1.5 in
  Finished height 0.75 in; stock thickness 0.789 in
  12 segments: long edge 1.784 in; short edge 0.995 in
  Strip width 1.473 in; strip length 23.858 in
  Finished outside envelope diameter 6.5 in; inside envelope diameter 4 in

Ring 3 — height band 1.5 in–2.25 in
  Finished height 0.75 in; stock thickness 0.789 in
  12 segments: long edge 2.052 in; short edge 1.383 in
  Strip width 1.249 in; strip length 27.073 in
  Finished outside envelope diameter 7.5 in; inside envelope diameter 5.5 in

Ring 4 — height band 2.25 in–3 in
  Finished height 0.75 in; stock thickness 0.789 in
  12 segments: long edge 2.186 in; short edge 1.642 in
  Strip width 1.016 in; strip length 28.681 in
  Finished outside envelope diameter 8 in; inside envelope diameter 6.5 in

Ring 5 — height band 3 in–3.75 in
  Finished height 0.75 in; stock thickness 0.789 in
  12 segments: long edge 2.186 in; short edge 1.771 in
  Strip width 0.774 in; strip length 28.681 in
  Finished outside envelope diameter 8 in; inside envelope diameter 7 in
No separate base blank included.
Rectangular stock: 0.810316 board ft; strip total: 127.328 in
Profile is piecewise linear. Confirm actual stock, saw setup and a test ring. No certification of glue, grain movement or safe machining.

Why the strip is wider than the finished wall

A polygon must enclose the round outside surface. Its inside opening must remain within the intended hollow surface. For each height band, this planner uses the largest outside radius and smallest inside radius along the whole profile band, then adds your turning allowances. Checking only the middle of a ring can miss a bend in the profile.

Worked example: a 240 mm ring

For 12 segments, outside diameter 240 mm and inside diameter 190 mm, with zero allowances, the miter setting is 15°. The long edge is 64.308 mm, the short edge is 49.176 mm and the radial stock width is 28.237 mm. Twelve long edges total 771.694 mm before kerf or trim. The 25 mm finished wall is not the stock width.

What this plan includes

The outer polygon's apothem is the maximum outside radius plus the outer allowance. The inner polygon's vertex radius is the minimum inside radius minus the inner allowance. For θ = 180° / segment count: long edge = 2 × outer apothem × tan θ; short edge = 2 × inner vertex radius × sin θ; strip width = outer apothem − inner vertex radius × cos θ.

Each separate-segment strip reserves segment count × (long edge + kerf / cos θ), plus your total end trim. Triangular offcuts are not reused. Stock volume uses rectangular strips and any separate square base blank; it is not finished bowl volume. One board foot is 144 cubic inches.

Planning the full profile and separate ring material is illustrated in the First State Woodturners introduction to segmented woodturning. Dedicated planning software also exists. This calculator focuses on simple horizontal closed rings, not open segmented designs, tilted staves or decorative pattern alignment.

Use the board foot calculator for other measured lumber. Bowl base dimensions, grain orientation and ring flattening need a separate construction decision.