How to use it

Enter the width of your circle in blocks. To make an oval, untick Keep it a circle and set the height too.
Pick a style:
- Thin: the outline steps diagonally from block to block, so some blocks touch only at their corners. It uses the fewest blocks and looks smoothest from far away. There's still no gap a player, mob or water can get through.
- Thick: every block touches the next along a full side. It uses more blocks but reads as a solid, even wall from both inside and out.
- Filled: the whole disc, for floors, ponds and the layers of a dome.
Hover over or tap the preview to see the column and row of any block, and how many blocks that row has.

Odd or even sizes?

Odd widths (like 21) have a single middle block. Easy to centre on a pillar, a beacon or a doorway.
Even widths (like 20) have no middle block: the centre falls on the seam between two blocks. Use these when the middle needs to be 2 blocks wide, such as a two-block entrance.

The dashed lines in the preview mark the centre, either through the middle block or along the seam.

Build one quarter, then mirror it. A circle is symmetrical, so count the blocks in one quarter from the preview and repeat it, flipped, for the other three.
Mark the centre first. Place a temporary block at the centre, then count outward along each row.
Use a scaffold line. Run a straight line of blocks across the full width, through the centre, before building the outline. It catches counting mistakes early.
For domes, stack filled circles that get smaller as you go up, and keep each layer's size odd or even to match the base.