Solving a 6×6 sudoku:
what 2×3 blocks change

The grid holds 36 cells and is filled with the digits 1 to 6. The rules do not change: every row, every column and every block contains each digit exactly once.

What changes is the shape of the blocks. Each is two rows tall and three columns wide, which gives six blocks arranged in three rows of two:

The six blocks of a 6×6 sudoku: two rows, three columns each.

Two consequences follow from that layout:

• a row crosses only 2 blocks, just like in an 8×8 — instead of 3 in classic sudoku;
• a column crosses 3, one fewer than on the 8×8 grid.

The 9×9 is symmetrical — rows and columns play the same role. The 6×6 is not, but the gap is milder than in an 8×8: it is a gentle first contact with the idea, before the 8×8 pushes it further.

Scanning is the basic technique: to place a digit inside a block, you rule out every cell whose row or column already holds that digit elsewhere. In a 9×9, ruling out a row or a column amounts to the same thing — 3 cells eliminated out of 9 either way.

In a 6×6, not quite. A block is two rows of three cells:

• ruling out a row eliminates 3 cells out of 6 — half the block at once;
• ruling out a column eliminates only 2 — a third.

Same free error check as elsewhere: since every block must contain the digit exactly once, that digit cannot sit outside the block on both of its rows at the same time. Seeing that configuration flags a digit misplaced earlier, not a broken puzzle.

Call a band a pair of side-by-side blocks — that is, two full rows of the grid. Each of those two rows holds the digits 1 to 6 once, so the band holds every digit exactly twice. And since each block holds it once, there is necessarily one in the left block and one in the right block.

Those two copies cannot share a row — that row would hold the digit twice. Hence the deduction, immediate and free, exactly as in an 8×8:

The 5 in the right block has to be on the bottom row. Three cells left to separate.

In classic sudoku, the same band has three blocks and three rows: placing a digit in one of them still leaves two possible rows for each of the other two. Here, just like in an 8×8, there is no choice at all — the constraint is total from the very first digit placed.

Top to bottom, the grid reads as two stacks of three blocks. A stack is 3 columns by 6 rows, so it holds every digit three times — once per block. But each of its three columns can hold it only once, so those three copies occupy the three columns, one each.

That is a strong constraint, and it pays off faster than in an 8×8: as soon as the digit is placed in two of a stack's three blocks (against three of four in an 8×8), its column in the third is already settled — it is the only one left free. Only two cells remain possible — the block's two rows — and the two-row rule often settles the second.

Combining the two is what cracks most Easy and Medium puzzles: the band gives you the row, the stack gives you the column, and the intersection gives you the cell. Without writing a single pencil mark.

Six candidates per cell is still manageable in your head on Easy puzzles, but it gets tighter from Medium onward. On Sudoku-Land, notes mode is one right-click away on any empty cell, or one tap on the dedicated button of the input ring.

Once the marks are down, the technique that pays best is the naked pair: two cells in the same block holding the same two candidates and nothing else. Those two digits are reserved for them, and vanish from the block's four other cells.

And it already pays more than in a square block, for a purely geometric reason. In a 2-by-3 block, two cells picked at random share a row 2 times out of 5 — against 1 out of 4 in a classic square block. A pair that lines up does not only eliminate inside its block: it eliminates along the whole row too. So just under one naked pair in two hands you that double effect.

1. Looking for squares. An eye trained on the 9×9 carves the grid into square blocks by itself, and gets it wrong one cell in three. Trust the thick lines, not your intuition.
2. Scanning by columns. It is the mirror reflex from classic sudoku, and here it yields a third less: two cells eliminated instead of three. Rows first, always.
3. Forgetting the neighboring block in the band. The two-row rule is the easiest gain on the board, and it is the one you skip when playing fast. Digit placed, glance next door.

Junior Sudoku 6×6 offers free puzzles at three levels — Easy, Medium and Hard — with notes mode, the 🆘 Help button which animates the grid to show what to do next, and a stats panel to track your progress.

If the 6×6 still feels easy, Junior+ Sudoku 8×8 pushes the same idea further, with 2×4 blocks and a sharper row/column imbalance — see our article Solving an 8×8 Sudoku. And if you are just starting out, Kids Sudoku 4×4 introduces the same reflexes on a smaller, square-block grid.