Is an odd or even circle better in Minecraft?

Neither is rounder. Choose odd when something belongs in the exact middle — a beacon, a pillar, a fountain jet. Choose even when the middle needs to be walkable or two blocks wide, such as a doorway, a 2-wide stair or a 2x2 shaft.

Why does my circle have no centre block?

Because the diameter is even. An even width has no single middle column, so the centre is a 2x2 square of four blocks. That is correct, not a bug in the blueprint.

Do spheres follow the same rule?

Yes, in all three directions. An odd diameter sphere has a single block at each pole and a true centre; an even one has a 2x2 pole cap and a 2x2x2 core.

Reference

Even vs odd Minecraft circles

The single most useful thing to know before choosing a diameter: whether you want a block in the exact middle.

5 minute read

The difference in one sentence

An odd diameter — 11, 15, 21, 25 — has a single block at the centre and a symmetry line running through it. An even diameter — 10, 16, 20, 30 — has no middle column at all; the centre is a 2 x 2 square, and the symmetry line runs along the seam between blocks.

Choose odd when the middle matters

A beacon, lantern or end rod that should sit dead centre under a dome.
A central pillar — a spiral staircase column, a tree trunk, a support post.
A single fountain jet or a one-block water source.
Anything you want to mirror. Odd widths mirror cleanly around one column, which makes it much easier to check a build for symmetry as you go.

Odd circles are also slightly easier to build by hand, because the widest row and the widest column cross at one identifiable block that you can place first.

Choose even when the middle is used

2 x 2 doors and archways lined up with the centre of a round wall.
2-wide staircases and 2 x 2 lift shafts through a tower.
2 x 2 fountain basins and pools, which fill more convincingly than a single source block.
Matching an existing even-width building. A 20-wide hall wants a 20-wide dome.

What does not change

Roundness does not depend on parity. Both odd and even circles are the best possible block approximation at their size, and the same algorithm produces both. What changes is where the symmetry lives, which affects how you build rather than how it looks.

Block counts, on the other hand, do not grow evenly. Going from an odd diameter to the next even one sometimes adds a lot of outline blocks and sometimes almost none, because the staircase gains a step in each quadrant or does not. The circle size chart shows this clearly.

A practical habit

Decide what goes in the centre before you decide the size. If the answer is "a block", round your diameter to the nearest odd number. If the answer is "a walkway, a door or nothing", use even. It is a two-second decision that saves rebuilding a tower one block wider later.

Both work in the circle generator, and the mirroring option adapts to whichever you pick — around the centre block for odd diameters, around the seam for even ones.