Pick a diameter and get a block-by-block circle with the number of blocks in every row. Even and odd sizes, filled or hollow, any wall thickness. Ovals, spheres, domes and cylinders too.
| Row (z) | Blocks | Runs |
|---|
Runs read left to right, alternating blocks and gaps: 2-6-2 = 2 blocks, 6 empty, 2 blocks.
| Layer | Blocks | Running total |
|---|
Set the width to the diameter you want, in blocks. Start from the centre of your build and mark the middle row first: the table under the grid gives the number of blocks in every row and how they are split, so a row reading 3-9-3 is three blocks, nine empty, three blocks. Hover or tap a block to see its coordinates from the centre (x across, z down, the way Minecraft's compass works with north at the top), then build row by row or work around the edge one quarter at a time. The guide lines every 5 and 10 blocks make it easy to count on the grid.
An odd diameter, like 21, has a single centre block, so coordinates run from −10 to +10 through 0. An even diameter, like 20, has no middle block: the centre is the corner where four blocks meet, so the middle of the circle is a 2×2 square and the coordinates run −10 … −1, +1 … +10 with no 0. Even circles suit builds centred on a 2×2 feature such as a double door or a 2×2 pillar; odd circles suit a single centre block like a beacon or a fountain.
Filled gives the whole disc, which you need for floors and roofs. Hollow gives just the outline, for walls and towers, and you can make it more than one block thick. A sealed outline never has two blocks touching only at a corner, which looks solid from every angle and keeps the inside fully enclosed; a thin outline uses fewer blocks. Switch to Sphere, Dome or Cylinder for 3D builds, shown one layer at a time.
A block is placed when the centre of that block lies inside the circle (or oval, sphere or dome) that exactly fits the width and height you chose. Outlines keep every block of the filled shape that is within your thickness of the outside: Sealed counts corner neighbours too, so the inside never touches the outside even diagonally and the wall has no diagonal gaps; Thin counts only side neighbours, which uses fewer blocks but lets wall blocks meet at a corner.