Sudoku Rules: How to Play Sudoku
Sudoku is a logic puzzle played on a 9×9 grid. You fill in the digits 1 to 9 so that every row, every column, and every 3×3 box contains each digit exactly once. The starting numbers are your clues, and a good puzzle has exactly one solution you can reach without guessing.
The grid
The grid has 81 cells: 9 across and 9 down. A horizontal line of cells is a row, a vertical line is a column, and each 3×3 block outlined in bold is a box.
There are nine rows, nine columns, and nine boxes, and every cell belongs to exactly one of each.
The three rules
1. Each row contains the digits 1–9 exactly once.
2. Each column contains the digits 1–9 exactly once.
3. Each box contains the digits 1–9 exactly once.
In other words, the same digit never appears twice in a row, column, or box. No arithmetic is involved.
How to start: follow one digit
Pick a digit that already appears many times on the grid. Imagine lines running across and down from each copy of it, and cross out the cells they pass through.
If a box is left with only one cell where that digit can go, that's the answer. This is called a Hidden Single, and it solves most of an easy puzzle on its own.
Using pencil marks (candidates)
When you're not sure about a cell, write the digits that could still go there in small print. Those are its candidates: every digit not already in the cell's row, column, or box.
When a cell has just one candidate left, it's solved (a Naked Single). In harder puzzles, patterns among the candidates — pairs, pointing, and so on — let you remove more of them.
When you get stuck
Go back through the digits one at a time. A missed Hidden Single is the most common reason for getting stuck.
If that doesn't help, fill in all the candidates and look for Pointing, then Box/Line Reduction, then pairs. The hints in the app and the browser version show you where to look next in three steps.
Frequently asked questions
Does a sudoku have only one solution?
A properly made sudoku has exactly one solution. The puzzles here are all checked to have a single solution that can be found by logic.
Do you need math for sudoku?
No. The digits are only symbols, so there is no adding or multiplying. (Killer Sudoku is a different variant that does use sums.)
How long does a sudoku take?
An easy puzzle takes around 5–15 minutes, and a hard one can take 30 minutes or more. You get faster at each difficulty with practice.
Where should I start solving?
Start with the rows, columns, and boxes that are most filled in, or with the digit that appears most often. Their missing spots are the quickest to pin down.