Themed Sudoku

What is themed sudoku?

Themed sudoku is classic sudoku with pictures in place of numbers. There are 21 themes here — holidays from Christmas to the 4th of July, the four seasons, space, dinosaurs, animals, dogs, food, music, sport and a rainbow of colours — and every one plays the same way. Fill the grid so that:

• every row holds each picture once;
• every column does too;
• and so does every box.

Each picture stands for a number, and the key under the board says which: in the Christmas game the Tree is 1, the Gift 2 and the Santa 3, on to the Cookie at 9. Sudoku never adds or compares its numbers, so nothing is lost in the swap: a picture is only a name for a value, and every deduction that works with digits works with pictures.

Pictures, numbers or both?

Every themed game has three buttons above the board. Pictures draws only the pictures, and pencil marks as small pictures too. Numbers turns the board into a plain sudoku: the pictures go, and the numbers they stand for take their place. Both, the view every game opens in, draws each picture with its number beside it. The view never touches the puzzle: you can switch halfway through a board and nothing moves.

Numbers are quicker to scan once you know sudoku; pictures make the board friendlier, especially for children. Both is the bridge between them: you can scan by number and still see the theme.

Which board size?

Each game deals three sizes. 4×4 uses the first four pictures, in boxes of two by two; 6×6 uses six, in boxes of two rows by three columns; 9×9 uses all nine, in the classic three-by-three boxes. Every game opens on 6×6 Easy, in Both. The level sets how many pictures you start with:

Pictures given at the start, from 40 boards per size and level dealt by the games’ own generator (fixed seed). At 4×4 and 6×6 singles alone finished every one of those 320 boards, so the levels there differ only in what you start with. At 9×9 they differ in the steps as well: singles alone finished 40, 40, 36 and 31 of the 40 Easy, Medium, Hard and Expert boards, and the rest needed locked candidates or, on Expert, a naked pair. Expert digs toward 22 and keeps the fewest of up to six tries: 22 to 24, median 23.

4×4 is the size for young children: four pictures and a board small enough to take in at once. 6×6 is a real puzzle without the full classic grid. 9×9 is classic sudoku in costume, and its Hard and Expert levels teach the same two moves as the classic board.

How do you solve one?

One picture at a time. Pick a picture, find every copy of it already on the board, and look at a box that still needs it: each copy rules out its own row and column. When only one empty square of the box is left, the picture goes there, whatever else that square could hold on its own. That is a hidden single, the move in the diagrams above. The same sweep works along a row or a column, and a square whose row, column and box already hold every picture but one takes that one.

Those two moves finish every 4×4 and 6×6 board, and every 9×9 Easy and Medium one. 9×9 Hard boards are dug so that singles and locked candidates finish them, and Expert boards so that singles, locked candidates and naked pairs do. For those, keep pencil marks: Notes draws them small in a square, and Auto Notes fills in every square at once. If you are stuck, Hint fills one square with its answer — a square picked at random, not the one you could work out next — and Undo can take it back.

Were the boards fair?

They always had exactly one answer: from the day the themed games went up, 12 to 14 June 2026, the generator checked every picture it took out with a full search, and we re-counted 480 of its boards — 40 per size and level — with a separate counter to confirm it. What it never checked was how a board would be solved, though this page told players that by the time they reached 9×9 they would have practised “checking constraints, finding missing symbols, using notes, and avoiding guesses”.

At 4×4 and 6×6 that did no harm: singles finished every board but one 6×6 Expert board in 40. At 9×9 each level only had a number of pictures to leave, as on the classic board. Expert aimed at 22, reached it on none of 40 boards and left a median of 25, much the same as Hard’s 26, and a solver that knows singles, locked candidates, pairs, triples and the X-Wing could not finish 28 of the 160 9×9 boards — 2 Medium, 10 Hard and 16 Expert. On those, avoiding a guess was not always possible.

The generator was rewritten in October 2026, with the same fix the classic board got. It now takes a picture out only while the level’s own steps still solve the board, which also proves the board has exactly one answer, and the steps mean the same at every size. A keyboard fault went at the same time: Ctrl+1 (Cmd+1 on a Mac) put the first picture in the selected square instead of switching browser tabs, and counted a mistake if it was wrong there. The Christmas card above also listed hats, lights and stockings the game never had; it now lists the nine pictures it does.

Where to go next

4x4 Sudoku and 6x6 Sudoku are the small boards in plain numbers, each with an article of its own. Emoji Sudoku and Symbol Sudoku are 9×9 picture puzzles with one set of nine all year round.