Planet Sudoku

How do you Sudoku? Introduction to How To's

Solving Techniques

Millions of Free Sudoku Puzzles 4x4, 6x6, 8x8, 9x9, 12x12, to 25x25 at Planet Sudoku!

Planet Sudoku's helpers section will improve your puzzle solving skills.

Show Hints / Candidates will help you see the available pencil values within the cell, row, column, and boxes.

How do you Sudoku? - How To Introduction and Strategy

Sudoku is a logical game that deals with process of elimination of invalid CELL possibilities. Once a player understands the logic of “this value can’t be there, therefor it could or must go here”, the game becomes pretty fun and challenging. You really do get a sense of accomplishment once you complete a puzzle.

There are several different types of Sudoku puzzles ranging from different sizes to even using letters. For a Sudoku puzzle to be valid you must have a unique number within a CELL inside an intersecting ROW, COLUMN, and BOX containers. Boards are made up of PEN values (gray cells that you cannot change), and you fill in empty CELLS with PENCIL values (cells that you can change). Valid CANIDATES or HINTS are unique penciled values that can be placed within a cell, which we will get to a little bit later.

What are CELLS, ROWS, COLUMNS, BOXES, and HINTS?
  • CELLS
    • Are the empty squares on the Sudoku board where you can enter penciled values (hopefully valid). Each cell has a unique name within the puzzle board. For instance most Sudoku boards name the cells based on the row and column they reside in. The name R1C1 refers to the first cell on the top left corner of the board. Because our system supports the ability to handle multiple Sudoku boards such as Sudoku Samurai which consists of five unique boards making up one puzzle. Because of this we added an additional identifier of “S”, meaning Sudoku board. So the same R1C1 will be S1R1C1 (Sudoku board 1, Row 1, and Column 1) within our board system.
  • ROWS
    • Are horizontal containers that when fully filled and valid, should contain a unique set of penned and penciled values for each cell within. Rows intersect with COLUMNS and BOXES.
  • COLUMNS
    • Are vertical containers that when fully filled and valid, should contain a unique set of penned and penciled values for each cell within. Columns intersect with ROWS and BOXES.
  • BOXES
    • Are containers that on a traditional Sudoku 9x9 board are composed of nine other cells. When fully filled and valid, should contain a unique set of penned and penciled values for each cell within. Boxes intersect with ROWS and COLUMNS.
  • BLOCK
    • Combination of ROW, COLUMN, and BOX CONTAINER of a specified CELL.
  • CONTAINER
    • Generic term for a ROW, COLUMN, or BOX.
  • HINTS / CANDIDATES
    • Are possible valid pencil values that can be placed within a cell. Hints values are only valid if there are no other pencil or pen values within the ROW, COLUMN, or BOX for that specific cell. Solving techniques such as hint reduction methods allow hints to be removed by applying solving logic as discussed later on.

Start playing Sudoku online today! We have many different boards and difficulty levels to choose from.