Summary: Jigsaw sudoku is sudoku with the boxes cut into interlocking shapes. The rows and columns behave exactly as you expect, but the nine 3×3 blocks are replaced by nine irregular regions that wander across the grid. This guide covers the goal, the rules that keep every board solvable by logic, the extra technique that irregular regions unlock, and where to try one in your browser.
Jigsaw sudoku is a sudoku variant in which the square boxes are replaced by irregular, interlocking regions. Each region still holds as many cells as the grid is wide, and still needs every digit once — but you can no longer scan a neat block, you have to follow an outline. That single change makes a familiar puzzle feel new, and it needs no arithmetic and no vocabulary: you only have to tell nine things apart, which is why jigsaw sudoku works just as well with letters, colours or pictures in place of the digits.
The Goal
Fill every cell with a digit so that each row, each column and each outlined jigsaw region holds every digit exactly once.
On a 9×9 board the digits are 1 to 9 and there are nine regions of nine cells. On a 6×6 board the digits are 1 to 6 and there are six regions of six cells.
Jigsaw Sudoku Rules
- Rows and columns are ordinary sudoku. Every row and every column contains each digit exactly once, exactly as in a standard grid.
- The regions replace the boxes. Each region holds as many cells as the grid is wide, and every digit appears once inside it. Regions never overlap, and every cell belongs to exactly one.
- Every region is one connected piece. You can walk from any cell of a region to any other cell of the same region by stepping between edge-sharing neighbours. There are no islands.
- No region is a straight row or column. A region that lined up with a whole row or column would just repeat a constraint you already had, so those layouts are rejected and a new shape is generated. Every region genuinely cuts across the grid.
- There is exactly one solution. Every board is verified before it is printed, so any answer that satisfies all the rules is the answer.
- You never have to guess. Each puzzle is confirmed solvable by human technique alone, at exactly the difficulty it claims. A stuck board means a deduction you have not spotted yet.
How to Solve Jigsaw Sudoku
- Trace the regions before you place anything. Spend the first thirty seconds following each outline with your eye. Irregular shapes are easy to misread mid-solve, and a digit placed in the wrong region is a mistake you will not notice for ten more moves.
- Scan for singles, exactly as you would on a normal grid. A single is either a cell with only one digit left open to it, or a digit with only one legal cell left in its row, column or region. These are the moves you will make most of the time; the only change is that the third house you scan is a shape rather than a block.
- Work the narrow regions first. A region squeezed into two or three columns has most of its digits forbidden already, because those few columns are shared by everything else in them. Fewer columns means fewer places each digit can go — so narrow regions fill earliest and give you the most.
- Use the region-and-line squeeze. If, inside one region, every remaining place for a 7 sits in the same row, then the 7 for that region is somewhere in that row — so it cannot be anywhere else in that row, inside or outside the region. This is the jigsaw form of the box-line rule you may know from standard sudoku, and because irregular regions overlap rows and columns in lopsided ways, it fires far more often here.
- Watch where a region narrows to one cell wide. A single-cell neck belongs to a row or column that is already carrying most of that region’s digits, so the intersection usually resolves in one step: whatever the row still needs and the region still needs is the same digit.
- When you stall, reach for the law of leftovers. It is the one technique jigsaw adds, and it is below.
The Law of Leftovers
This is the signature jigsaw technique, and the one worth practising.
Take a band of rows — say the top three rows of a 9×9 board. Those 27 cells hold 1 to 9 three times over. Now choose exactly three regions — the same number of regions as rows in the band. Those three regions also hold 27 cells, and also hold 1 to 9 three times over.
The two sets therefore cancel. Whatever cells of your three regions fall outside the band hold exactly the same digits as the cells inside the band that belong to none of the three. The two leftover sets always contain the same number of cells, which is your check that you picked the regions correctly.
The prize is the one-against-one case. Choose the three regions that overlap the band most heavily, and the leftovers often shrink to a single cell on each side — and those two cells must then hold the same digit, so knowing either one hands you the other for free. Two against two is still worth having: you learn which pair of digits sits in those two cells on both sides, even though you do not yet know the order.
Two practical notes. The band does not have to be at the top — for a middle band, “outside” means above and below, and you count both. And the same trick works on columns: choose a band of columns and the same number of regions. On a 6×6 board, use two rows (12 cells, 1 to 6 twice over) and exactly two regions.
Layout Styles and Sizes
Region layouts come in two styles. Symmetric layouts — the standard — are built so the pattern reads the same after turning the page 180°, which is the look published jigsaw sudoku has always had. Random layouts drop the symmetry for free-form shapes with a rougher, more organic feel. Both play by identical rules; the difference is entirely in the look.
The 9×9 board is the standard jigsaw sudoku. The 6×6 board uses digits 1 to 6 across six regions — a much shorter solve, and the friendlier introduction for younger solvers, for a warm-up page, or for a class working inside one lesson.
Difficulty runs across seven graded levels — Very Easy, Easy, Normal, Hard, Very Hard, Tough and Extreme — and the grade describes the hardest technique the board actually requires, not how few digits it starts with. New to jigsaw sudoku? Start at Easy on a 6×6 and move up once tracing the regions stops feeling like work.
Try It Online
Jigsaw sudoku plays well in a browser: click a cell and type a digit, and clear it as easily when a region turns out to have needed that digit elsewhere. The bold outlines stay visible on screen, so you can follow a region’s shape without tracing it with a finger. Play a jigsaw sudoku in your browser — no download, no sign-up. The general player controls — checking your answer, resetting, the timer, and working through a set — are covered once in How to Play Puzzles Online.
You Are Ready to Play
You now know what a jigsaw sudoku is asking for, the rules that keep every board fair — connected regions, no region that copies a row or column, one solution, no guessing — and the routine that cracks them: trace the shapes, scan for singles, work the narrow regions, squeeze regions against lines, and reach for the law of leftovers when the easy moves run out. Ready to make your own? See How to Create Jigsaw Sudoku Puzzles in Puzzle Maker Pro.
FAQ
Is jigsaw sudoku harder than normal sudoku?
At the same graded level it is meant to ask about the same of you: the grading is deliberately compensated for how much slower irregular regions are to scan. What changes is the feel. Pattern recognition helps less, and careful region tracing helps more.
What is the law of leftovers in jigsaw sudoku?
Choose a band of rows and the same number of regions. The cells of those regions that fall outside the band hold exactly the same digits as the cells inside the band belonging to none of them. When each side comes down to a single cell, those two cells must hold the same digit; with more cells on each side you learn which digits are shared, but not yet which cell takes which.
Can a jigsaw sudoku have more than one solution?
No. Every board is verified to have exactly one solution before it is printed.
Do the regions ever repeat between puzzles?
Each puzzle gets its own freshly generated layout, and no two boards in a single run repeat, so a jigsaw sudoku collection stays visually varied from page to page.
Why is the region pattern symmetrical?
That is the symmetric layout style, the one published jigsaw sudoku has traditionally used: turn the page 180° and the pattern matches itself, with each region landing on its partner across the centre. The random style drops that symmetry for free-form shapes.
Do standard sudoku techniques still work on a jigsaw grid?
Yes, all of them. Singles, pairs and triples work exactly as they do on a normal grid — you just apply the region ones to a shape instead of a block, and the region-and-line squeeze is the jigsaw form of the box-line rule. The law of leftovers is the one technique jigsaw adds.