Sudoku Tips

Tip 1: Scanning – find single numbers fast – Always start by scanning rows, columns, and 3×3 boxes that already contain five or more filled numbers. The more numbers an area contains, the easier it is to work out which digit is missing. A row with eight numbers filled in has only one possible value for the empty cell — as long as the column and box confirm it.

Tip 2: The three-band method – Divide the board into three horizontal bands of three rows each (rows 1–3, 4–6, 7–9). If a digit, say 7, already appears in two of the three rows within a band, you know 7 must sit in the third row of that band. Combine this with column information to pinpoint the exact cell.

Tip 3: Write down candidates – Experienced solvers always note possible numbers (candidates) in every empty cell. A cell with candidates [1, 4, 7] can only be 1, 4, or 7. Each time you fill in a number anywhere on the board, cross it off as a candidate from that row, column, and box. When a cell’s candidate list shrinks to one digit, you have your answer.

Tip 4: Naked singles — the lone candidate – A naked single occurs when an empty cell has only one possible digit remaining after eliminating all numbers in its row, column, and box. It is the fastest and most common solving technique. Always search for naked singles before trying more advanced methods — finding one often unlocks a chain of further answers.

Tip 5: Hidden singles — the hidden lone number – Sometimes a digit can only be placed in one cell within a row, column, or box — even though that cell appears to have multiple candidates. Work through each digit (1–9) for every row, column, and box and ask: "Is there only one cell in this group where this digit can go?" If yes, fill it in right away. This is one of the most important foundational techniques.

Tip 6: Work in the most filled regions first – Always begin in the rows, columns, and boxes that already contain the most numbers. These regions provide the most constraints and make it easiest to deduce the next digit. Half-empty boxes give too little information to draw reliable conclusions and will cost you more time than they are worth at that stage.

Tip 7: Do not guess — take a break instead – Guessing in sudoku almost always leads to errors that propagate through the board and make the puzzle impossible to solve correctly without starting over. If you get stuck, step away for a few minutes and return with fresh eyes. You will almost always spot what you missed as soon as you look again.

Tip 8: Practice at the right difficulty level – Master scanning, naked singles, and hidden singles at easy and normal difficulty before moving up. Advance a level only when you can solve puzzles without getting stuck. Hard and extreme puzzles require locked candidates, X-Wing, and XY-Wing — techniques covered in our complete sudoku strategy guide.