Bowl Segment Calculator

A segmented bowl ring is a flat polygon of wedge-shaped pieces glued edge to edge. The layout comes from the outer diameter and the number of segments. The miter angle for each cut is 180 divided by the number of segments, and each segment has two of these cuts, so the included wedge angle is 360 divided by the segments.

The length of a segment along its outer edge is the diameter times the tangent of 180 divided by the segments; the inner edge is shorter, using the inner diameter.

For example, a 10 inch ring of 12 segments has a 15 degree miter, a 2.68 inch outer edge and a 2.14 inch inner edge on a 1 inch wall. This calculator gives the angle, the segment lengths and the board you need from your ring size and segment count.

The miter angle for each cut is 180 degrees divided by the number of segments in the ring. Each segment is cut at that angle on both ends, so the two cuts add up to the 360-over-N wedge that lets the pieces close into a full circle.

More segments mean a smaller miter angle and shorter pieces; fewer segments mean a larger angle. A 12-segment ring, the most common, is cut at 15 degrees; an 8-segment ring at 22.5 degrees; a 16-segment ring at 11.25 degrees.

For example, a 12-segment ring needs the saw set to 15 degrees. This calculator gives the exact miter angle for any segment count from 3 to 48, and the segment lengths to go with it.

Each segment has two lengths — the long outer edge and the shorter inner edge. The outer edge is the outer diameter times the tangent of 180 divided by the number of segments; the inner edge is the same formula using the inner diameter, which is the outer diameter minus twice the ring’s wall width.

You cut the board to the outer length at the miter angle, and the inner edge comes out shorter automatically because of the taper of the wedge.

For example, a 10 inch ring of 12 segments with a 1 inch wall has a 2.68 inch outer edge and a 2.14 inch inner edge. This calculator gives both lengths for your ring, so you can set a stop block to the long edge.

Twelve is the most common and a good default — it balances a reasonably round ring against a manageable number of joints. More segments, like 16 or 24, give a rounder ring and shorter pieces but more glue joints and more cuts to get exactly right; fewer, like 8, means longer pieces and fewer joints but a more faceted ring.

The segment count also sets the miter angle and the piece length, so it drives the whole cut list.

For example, a 10 inch ring is 12 segments at a 15 degree miter by default, but you can run 8, 16, 24 or any count from 3 to 48. This calculator recalculates the angle, lengths and board for whatever count you choose.

The board length for one ring is the number of segments times the outer segment length, plus an allowance for the saw kerf and trimming — about 15 percent extra. Multiply by the number of rings for the total board to buy.

Using the long outer edge and adding waste makes sure you have enough once the kerf of each cut and a little trimming are accounted for.

For example, a 10 inch, 12-segment ring needs about 37 inches of board per ring with the 15 percent allowance; six of those rings is about 222 inches total, or roughly 72 segments. This calculator totals the board length and segment count for your whole stack.

Almost always because the miter angle is slightly off. In a 12-segment ring, each of the 24 cuts must be dead on 15 degrees; any error is multiplied by 24 around the ring, so even a fraction of a degree per cut opens a visible gap or leaves the ring unable to close.

The fix is a precise, repeatable setup: a dialed-in miter gauge or sled, a stop block so every piece is identical, and a test ring assembled dry before gluing. Trimming a dry-fit ring to close it is normal.

For example, a 12-segment ring needs every cut at exactly 15 degrees. This calculator gives the exact angle and equal segment lengths; the accuracy of the cut is up to your setup, so test-fit before glue-up.

They are the two parallel edges of each wedge-shaped segment. The outer length is the long edge, on the outside of the ring; the inner length is the short edge, on the inside. The difference comes from the taper of the wedge, set by the wall width.

The outer edge uses the full outer diameter; the inner edge uses the inner diameter, which is the outer diameter minus twice the wall width. A wider wall makes the inner edge shorter relative to the outer.

For example, a 10 inch ring of 12 segments with a 1 inch wall has a 2.68 inch outer edge and a 2.14 inch inner edge. This calculator reports both, so you can mark or set a stop to the outer edge and check the inner.

Yes. Cut the ring a little larger than the finished diameter so you have material to turn away on the lathe and to true up the ring after glue-up. Segmented rings are rarely perfect off the saw, and you need stock to clean up the inside and outside to a smooth circle.

A common approach is to add some to the diameter and plan the wall a touch wide, then turn down to the finished size once the ring is glued and mounted.

For example, if you want a 10 inch finished ring, cut the segments for a slightly larger circle so there is turning allowance. This calculator works from the diameter you enter, so enter the cut size (a bit oversize) rather than the final turned size.