Windmill Sudoku Rules and Strategy for the Five-Grid Pinwheel

What is windmill sudoku

Windmill sudoku is an overlapping-grid variant built from five separate Sudoku boards. Four grids sit at the top-left, top-right, bottom-left, and bottom-right positions, and a fifth grid is placed in the middle so that each corner grid donates one of its 3x3 boxes to that central grid. The finished layout looks like the four sails of a windmill turning around a hub, which is exactly where the name comes from. Every one of the five grids is a complete, ordinary Sudoku, and the shared boxes are the hinges that hold the whole construction together.

The rules of windmill sudoku

• Each of the five 9x9 grids must contain the digits 1 to 9 exactly once in every row, once in every column, and once in every 3x3 box.
• The four outer grids overlap the central grid at one 3x3 box each, and the cells inside a shared box must obey both grids at the same time.
• A digit placed in a shared box counts toward two grids at once, so it has to be legal in both of them.
• A well-made windmill sudoku has a single unique solution that pure logic can reach without guessing.

The shared corner boxes are what make windmill sudoku more than five puzzles printed near each other. Because a number you place in an overlap has to please two grids, information flows across the seams. A clue in one grid can quietly eliminate candidates in a neighbor grid several steps away, and that chain reaction is the whole point of the variant.

A solving order that works

1. Start inside the four shared corner boxes. They receive constraints from two directions, so they are usually the most heavily restricted cells on the entire sheet.
2. Solve one outer grid as far as ordinary logic allows, then carry every confirmed digit in its shared box straight into the central grid.
3. Work the central grid using the fresh numbers from all four overlaps at once, since it is fed from every side.
4. Bounce back to the outer grids with the central answers you just found, and repeat the loop until each grid closes.

Why the overlaps make it easier, not harder

New solvers often expect windmill sudoku to be brutal because there are five grids, but the overlaps actually hand you extra leverage. A single shared box gives you eighteen row and column constraints instead of nine, so the corner boxes tend to collapse fast once you commit to them. Treat the puzzle as one connected system rather than five chores, keep a light pencil mark habit, and the pinwheel tightens on itself. If you get stuck, look for a digit that is nearly placed in one grid, because finishing it often unlocks the neighbor through the shared cells.

Sharpen the single-grid logic first

Every windmill sudoku is only as solvable as your comfort with one ordinary 9x9 board, since the variant just chains that skill five times. Shapedoku is a good place to build that core habit, because it swaps the digits 1 to 9 for nine glowing shapes while keeping classic Sudoku rules intact. The scanning instinct you train there, spotting where a symbol can and cannot go, is the same instinct that reads the seams of a windmill grid. Practice clean single-grid solving, then bring that confidence to the pinwheel.