Minecraft builds are made of cubes, so a circle on the ground is a decision about which squares belong inside a round outline. This generator uses the midpoint circle and ellipse rules for flat shapes: the same integer steps a graphics routine uses when it has to pick pixels. Thickness 1 keeps that outline. Thickness 2 and up adds the next outline inward, which is the usual way to fatten a wall without filling the courtyard. A sphere or dome uses a different test. A block stays if its distance from the centre, measured with x² + y² + z², sits in the shell between the inner radius and the outer radius. The layer slider then shows one horizontal slice, with a count beside every Y level, so you can build from the floor up and know when a layer is finished.
Load the example on a circle and you get radius 8, one block thick, with numbers on. The grid is centred on the block marked as the origin. Row counts underneath tell you how many blocks sit on each east-west line. If you are laying a ring and you lose count, the row total is the check, not the feeling that the left side "looks" like the right side. Numbers, when you ask for them, walk around the blocks by angle. They are a label so a screenshot can be discussed ("place through 12, then stop"). They are not a claim that some famous chart numbers the blocks in that order. The same outline opens on three pages: stairs and slabs, numbers, and thickness.
Ovals need two radii because a stretched circle is not a circle with one of the axes ignored. An 8 by 5 ellipse is wider than it is tall. The dedicated oval page starts in that mode. Spheres and domes share the shell test. A dome keeps only the layers where Y is zero or positive, which is the upper half including the equator, the usual choice for a roof. A full sphere includes the underground layers too. Switch to the sphere page if that is the only shape you want indexed later. Radius for a sphere stops at 32 because a solid ball of that size is already thousands of blocks and the grid is there to be read by a person.
How to build from the picture: stand on the centre block, face a cardinal direction, and count out to the radius along that line. The outermost block on the axis is the radius you typed. Then follow one row at a time, matching the count in the table. For a sphere, do the bottom layer first if you are digging, or the equator first if you are drawing the widest ring in the air and filling toward the top. The PNG is the same view, with the paper colour behind it, so it stays readable in a dark inventory screen. It is produced on your device. Nothing about the shape is uploaded.
Thin circles of radius 1 or 2 look clumsy. There are not enough blocks to fake a curve, and the midpoint rule will give you a plus or a small diamond. That is honest. If you need a round well, start nearer radius 6 or 8. Thick mode at a high thickness becomes a disc or a ball; the inner hole disappears once the thickness reaches the radius. A hollow tower is thickness 1 or 2. A filled landing pad is a large thickness.
The generator does not know about slabs, stairs, walls, or glass panes. Every cell is a full block. If you replace the top of a dome with slabs, the count on that layer is a maximum, not the slab count. It also does not rotate the shape for a diagonal build. The grid is aligned to the axes. Diagonal circles are a different pattern and are easy to get wrong by eye; this tool will not pretend to draw them.
Odd radii and even radii both work. The centre is a block, not the corner between four blocks. If your build's centre is a shared corner, shift the whole plan by half a block in your head and accept that this grid is the block-centred version. The outline is symmetric: every block has its mirror through the origin. If a row count on the left disagrees with the right, the browser tab is showing a stale result. Hit build again.