Build Circles in Minecraft
A circle in Minecraft is not a curve, it is a grid of square blocks approved or rejected one by one against the circle equation. That rasterization is why every block circle looks slightly jagged near the edges, even at large diameters.
The 11×11 grid has one exact center cell, giving the circle a perfect axis of symmetry across the 4 quadrants around that center block.
The 10×10 grid has no single center cell: the 4 blocks nearest the middle stay symmetric to each other, with none sitting at the exact position.
Only edge blocks are included, and the total comes out equal for diameter 10 and 11 at this size, because the rasterized perimeter of both converges to the same count.
Pick the diameter you want, generate the outline grid and reproduce the pattern block by block in-game, usually starting from the four cardinal points (top, bottom, left and right) and following the curve. To skip counting blocks by hand, copy the ready /fill commands (relative coordinates) and paste them into the game chat. The larger the diameter, the smoother the circle.
Because every block is an all-or-nothing test against the circle equation: there is no partial block, so the continuous curve becomes a stepped approximation, more visible at small diameters and smoother as the diameter grows.
Yes: an odd diameter gives an exact center block, useful as a reference point for aligning towers or domes; an even diameter has no single such block, but still keeps perfect symmetry across the 4 center-most blocks.
Diameter ranges from 1 to 150 blocks. Diameters far beyond that stop being practical to build by hand, and the block grid gets too heavy to render as text.
It depends on the diameter: at 11 blocks, the filled version uses 97 against the outline's 28, almost 3.5 times more material, because the outline only covers the outer shell while the filled version occupies the entire interior.
Generates ready /fill commands (coordinates relative to the player) so the game builds the pattern for you; stand at the center of the circle before pasting them in chat, and you need operator permission.
The grid is computed locally in the browser; nothing is sent to servers.