Choose a diameter and step through the sphere one layer at a time. Every layer shows its blocks, the blocks per row, and the running total.
| 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 |
|---|
A sphere is a stack of circles that grow towards the middle and shrink again. Start at layer 1, the bottom, build what the grid shows, then move up a layer with the slider or the + button. With "show the layer below" ticked, the layer you just built is drawn faintly underneath so you can line the next one up. The layer table lists the blocks in each layer and a running total, so you know how many blocks to bring.
Hollow spheres keep only the shell. In a hollow sphere the layers near the top and bottom are solid discs, because every block there touches the outside from above or below; that is what makes the shell closed. Sealed walls are watertight even at corners; thin walls use fewer blocks. Use Print to get every layer on paper.
An odd diameter has a single widest middle layer; an even diameter has two identical middle layers. Either way the very top and bottom layers are small flat discs rather than a single block (a 21-block sphere starts with 37 blocks), because a block is only placed where its centre is inside the sphere. For a dome, build the top half only.
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.