Hidden Quad
Four digits confined to the same four cells of a house, clearing all other candidates.
Also known as: Concealed Quad
Quick Summary
When four digits appear only within four cells of a house, those cells are locked for those four digits. All other candidates in those cells are eliminated.
Understanding the Hidden Quad Technique
Hidden Quads are the hidden counterpart to Naked Quads. They occur when four digits are restricted to four cells within a house. Because finding a Hidden Quad in a house with six empty cells is the exact mirror of finding a Naked Pair in the other two cells, skilled solvers often look for the smaller pair instead.
Visual Examples
Green cells highlight the Hidden Quad pattern, amber cells denote where candidates are affected, and struck-through pencil marks show the eliminations. Use the buttons or arrow keys to browse examples.
How to Spot & Solve a Hidden Quad (Step-by-Step Guide)
The complete visual scanning and logical deduction process to execute this technique:
- 1Identify four digits that appear only within four specific cells of a row, column, or box.
- 2Ensure that none of those four digits appear in any other cell of that unit.
- 3Those four numbers must fill those four designated cells.
- 4Erase all other candidate notes from those four cells.
Common Traps & Mistakes to Avoid
- Spending too much time hunting for hidden quads when checking the remaining cells for a naked pair is much quicker.
- Failing to verify that none of the four digits leak into a fifth cell.
Frequently Asked Questions
Is it better to look for Hidden Quads or Naked Pairs?
In a house with 6 empty cells, a Hidden Quad and a Naked Pair are two sides of the same coin. Looking for the 2-cell Naked Pair is almost always faster and less error-prone.
Related Solving Techniques
Expand your repertoire by learning prerequisites and advanced counterparts:
Ready to Practice Hidden Quad?
Try a puzzle in the Hard tier (Peak Score 51–60), or browse all 25 techniques.