Cross-Hatching and Scanning: How to Spot the Next Number Fast

Cross-hatching is the single most useful scanning skill in Sudoku. It's how experienced solvers place numbers quickly without writing a single pencil mark. Once it clicks, easy and medium puzzles get dramatically faster.

What is cross-hatching?

Cross-hatching means using the rows and columns that pass through a box to eliminate where a digit can go inside that box. You mentally 'strike out' the rows and columns that already contain the digit, and see which cells survive.

1. 1

   Pick a digit to place

   Choose a digit that already appears several times on the board — more copies means more eliminations.

2. 2

   Choose a box missing that digit

   Find a 3×3 box that doesn't yet contain your digit.

3. 3

   Strike out rows and columns

   Any row or column running through the box that already has the digit is eliminated. Cross those cells off in your mind.

4. 4

   Check what remains

   If only one cell in the box survives, that's a hidden single — place the digit there. If two or three remain, move on and come back after more placements.

What to do when scanning stalls

Scanning alone solves easy puzzles and gets you a long way into mediums. When you stop finding placements, that's the signal to switch tools:

• Start pencilling candidates into the remaining empty cells.
• Look for naked and hidden pairs among those candidates.
• Rotate your focus — switch from boxes to rows to columns; a placement you missed is often hiding in the direction you weren't checking.

Is cross-hatching the same as scanning?

Cross-hatching is a specific scanning method that uses intersecting rows and columns to pin down a digit inside a box. Scanning is the broader habit of sweeping the grid for placements.

Can I solve a whole puzzle with cross-hatching alone?

Easy puzzles, yes. Medium and hard puzzles eventually need pencil marks and candidate-based techniques once cross-hatching runs out.