Sudoku Step by Step: Solve Your First Full Puzzle

Reading about sudoku techniques helps, but the fastest way to see how a real solve unfolds is to watch the actual move list. So we let this site's engine generate 320 puzzles — 80 at each difficulty — and logged every step it took to finish: 320 full solve ledgers, 15,520 recorded moves in total. The pattern that emerged does not match what most tutorials imply.

A full puzzle is not 81 separate decisions. It is a short move list, and its length is settled before you start.

A Full Solve Is 41 to 55 Moves — the Clues Set the Length

Every solving step fills exactly one cell, so a 9x9 puzzle always needs 81 minus its clue count in moves. The difficulty setting on the generator really just picks the clue budget: easy puzzles come out with 40 clues (41 moves), medium with 34 (47 moves), hard with 30 (51 moves), and evil with 26 (54–55 moves).

| Difficulty | Mean clues | Mean moves | Naked single | Hidden single | Search | |:-----------|:----------:|:----------:|:------------:|:-------------:|:------:| | easy | 40 | 41 | 100% | 0% | 0% | | medium | 34 | 47 | 95.7% | 3.8% | 0.5% | | hard | 30 | 51 | 81.3% | 11.8% | 6.9% | | evil | 26 | 55 | 61.3% | 18.8% | 19.8% |

Two takeaways hide in this table, and they point the same direction. As difficulty climbs, non-single techniques eat into the naked-single share — from zero on easy to 38.7% on evil. But even on the hardest tier, more than six of every ten moves are the simplest placement in the game: a cell with one legal digit left.

The Chain Reaction Is Real: One Cascade Carries Half the Board

The "sudoku solves itself" feeling is not nostalgia. We measured the longest run of consecutive single placements inside each ledger. On easy puzzles the entire solve is essentially one unbroken chain — an average longest run of 40.8 out of 41 moves, with every one of the 80 puzzles solved entirely by naked singles. Medium and hard grids still deliver a single chain of roughly 47 placements, and evil grids pair their search moves with a run of 43.5 back to back. Ground covered: the longest chain in a solve fills 51% to 58% of the board at every difficulty. Even on evil, 94% of puzzles contain a run of ten or more unbroken placements, and 79% contain a run of twenty.

Here is that chain on a real easy puzzle, a 40-clue grid straight from the generator:

0 6 0 0 9 7 1 0 0
0 0 5 0 2 4 9 8 0
0 4 0 0 1 5 3 0 0
0 0 3 7 5 2 8 0 0
0 0 0 1 0 6 2 0 5
0 0 8 4 0 0 0 0 0
4 8 0 0 0 0 5 7 0
3 2 6 5 0 8 0 9 1
5 7 0 0 0 3 6 2 0

The solver's first eight moves, verbatim:

1. r1c3 = 2 — only one candidate left
2. r1c1 = 8 — only one candidate left
3. r1c4 = 3 — only one candidate left
4. r1c9 = 4 — only one candidate left
5. r1c8 = 5 — only one candidate left
6. r2c4 = 6 — only one candidate left
7. r2c9 = 7 — only one candidate left
8. r2c1 = 1 — only one candidate left

Step 41 repeats the same move as step 1, and nothing in between is anything else. There is no technique switch on this board because there is nothing to switch to.

Real talk: that reads anticlimactic until you hold a real grid. Beginners stall on easy puzzles almost never because a technique is missing — the ledger says every cell is a naked single. They stall because they do not re-check the row, column, and box after each placement. The chain breaks when you stop scanning, not when the puzzle stops cooperating.

Hard Moves Arrive Late — or Not at All

Hidden singles and search steps are the slow part of the ledger, and they are also the late part. Hidden singles climb from zero per easy puzzle to 1.8 on medium, 6.0 on hard, and 10.3 on evil. Search appears in 0 of 80 easy puzzles, 1 of 80 medium, 9 of 80 hard, and 22 of 80 evil. When it does appear, it lands deep: 64% of the way through that single medium solve, 41% through hard ones on average, and 30% through evil ones.

The two halves of a ledger mirror that from the other side. Non-single moves in the first half: 0.8 per hard puzzle and 3.6 per evil puzzle. Second half: 2.7 and 7.3. The moves that need real thinking cluster in the endgame, which is exactly where a tired solver starts guessing.

One grid in the sample broke this pattern hard, and it is worth knowing about. An evil puzzle stalled after just 10 logical moves — 4 naked singles and 6 hidden singles — then finished its remaining 45 cells with pure trial and error. No technique inventory would have saved it; the logic simply ran dry before the board was a quarter full. When a puzzle feels like that one, the answer is not another pattern to memorize. It is a hint.

The Ledger Versus the Technique Hunt: Where Practice Time Goes

Most tutorials sell techniques as the cure for difficulty. The measured ledger suggests the opposite split. On easy and medium puzzles, roughly 96–100% of moves are single placements — a beginner who scans properly and keeps pencil marks is already solving those completely. Studying X-Wing to beat a medium puzzle is buying a chainsaw for a plant that needs water.

Difficulty earns its name in the hidden-single ramp and the search tail, and that is where the step-by-step approach earns its keep. Following a solver one move at a time shows you which scan you skipped: a hidden-single step names the digit and the unit it hid in. Run that comparison for 20 or 30 puzzles and the endgame scan becomes automatic.

The practical version of this is the hint-tap economy. Finishing a puzzle with a hint at every move costs 41 taps on easy, 47 on medium, 51 on hard, and 55 on evil. Start each solve unaided, tap only where you genuinely stall, and compare the engine's move with what you were staring at. That comparison is the entire skill.

Train With the Real Ledger

The fastest training loop is the one the numbers describe:

1. Generate a puzzle at your level in the sudoku maker — easy puzzles are one continuous chain, so they make the right first reps.
2. Mark candidates in every empty cell. The ledger depends on them: every hidden single in the sample is invisible without marks.
3. Place everything you can, re-scan after each placement, and when the chain breaks, take one hint from the hints tool and compare.
4. After 20 easy solves without a stall, drop to medium; the hidden-single ramp is the difference.

A complete sudoku solve is a 41-to-55-entry ledger, more than half of it one cascade, with the hard moves last if they come at all. The quickest way to trust that is to watch one ledger from start to finish — grab the sudoku guide if you need the rules first, then the logic breakdown for the late-game patterns, then run the loop above until the chain extends on its own.