Jigsaw Sudoku Rules: How Irregular Regions Work

The grid

Jigsaw Sudoku uses the same 9x9 grid as Classic Sudoku — 81 cells, same rows, same columns. What's different is the third grouping: instead of nine uniform 3x3 boxes, the grid is divided into nine irregular regions, each covering exactly 9 cells. Every region is shaded a different tint and outlined with a thick border so it's easy to trace its shape at a glance, even though no two regions look alike.

The rules: same three groups, one reshaped

Fill the grid with the digits 1 through 9 so that:

• • Each row contains 1–9 exactly once — no repeats.
• • Each column contains 1–9 exactly once — no repeats.
• • Each irregular region (9 connected cells) contains 1–9 exactly once — no repeats.

That's the entire rule set — genuinely identical in structure to Classic Sudoku, with the box rule simply reapplied to a different-shaped group of 9 cells. A region has to be a single connected shape (every cell touching at least one other cell in the same region edge to edge), and it very often stretches across what would have been two or three separate 3x3 boxes in the standard layout.

A worked example

Look at the highlighted region in the image above. It's a zigzagging shape that dips through parts of four different rows and three different columns — nothing like a tidy square — but it still holds exactly 9 cells, and every one of those cells still needs to end up with a different digit from 1 to 9, no repeats. The highlighted row and column work exactly as they would in Classic Sudoku: count what's already placed, and whatever's left has to go somewhere in the remaining empty cells.

The only real adjustment for solving is visual: before you can apply region logic to a cell, you have to trace its region's actual boundary rather than assuming a 3x3 square. Once you've done that, every technique from scanning to naked pairs carries over unchanged — see our solving techniques guide for the full method list.

Why irregular regions change the feel

Removing the fixed 3x3 boxes removes a mental shortcut most Sudoku players rely on without noticing: knowing exactly which nine cells a box covers without having to look. In Jigsaw Sudoku, a region can be tall and thin, an L-shape, or a scattered zigzag, so you have to actually trace its outline before you can reason about it — which slows down scanning at first but tends to reveal deductions a rigid box shape would hide. A region that pokes deep into an otherwise sparse row, for instance, can sometimes pin down a digit long before the row itself is anywhere close to full.

Notes (pencil marks)

Notes work exactly as they do in Classic Sudoku: toggle notes mode and tap a candidate into a cell as a reminder rather than a commitment. The one habit worth building specifically for Jigsaw Sudoku is double-checking a cell's region before ruling out a candidate — it's easy to mentally default to "3x3 box" out of habit and eliminate a digit for the wrong group of cells.

Difficulty levels

Difficulty is set by how many of the 81 cells are given as starting clues — the same clue counts as Classic Sudoku, since the row and column rules carry most of the same weight regardless of region shape:

Common rule mix-ups

• • Assuming a region looks like a 3x3 box — it almost never does. Always trace the actual colored/outlined shape before applying region logic to a cell.
• • Expecting regions to line up with box rows — a single region can, and usually does, span cells from what would be two or three separate 3x3 boxes in Classic Sudoku.
• • Thinking diagonal touches count — a region is only connected through shared edges. Two cells that only touch at a corner are not automatically part of the same region.
• • Forgetting rows and columns are unchanged — the region shape is the only thing that's different; row and column logic works exactly like Classic Sudoku.

Frequently asked questions