Naked Quad
Four cells in a unit whose candidates together use only four digits lock those digits out of the rest of the unit.
A naked quad is the four-cell extension of the naked pair and triple. Four cells in one unit have combined candidates drawn from exactly four digits, so those four digits must occupy those four cells — and can be removed from every other cell in the unit.
Quads are rarer and harder to see than pairs and triples, but the logic is identical: count distinct digits across the group, not candidates per cell.
How to spot it
Look for four cells in a unit whose pooled candidates contain exactly four distinct digits. Each cell may show two, three, or four of them. Those four digits are confined to those four cells, so erase them from the rest of the unit.
- Four cells, four digits total across them.
- Every cell’s candidates are a subset of those four.
- Eliminate the four digits everywhere else in the unit.
Worked example
- A column has four cells showing {1,4}, {4,7}, {1,8} and {7,8}.
- Their union is exactly {1,4,7,8} — four digits, four cells.
- The quad is locked, so 1, 4, 7 and 8 leave the rest of the column.
- A fifth cell showing {2,4,7} drops to {2}.
- Place that naked single and continue.
Try it yourself
Tap a cell, then a number, to practise.
Frequently asked questions
- How is a naked quad different from a hidden quad?
- A naked quad is identified from the cells (four cells using four digits); a hidden quad is identified from the digits (four digits confined to four cells, even if those cells carry extra marks).
- Is a naked quad worth hunting for?
- Only after singles, pairs and triples stall. With full pencil marks a quad usually announces itself as a tight cluster of low-candidate cells.
Related techniques
Practice: Naked Quad
Put the Naked Quad to work on a live board — free puzzles with notes, hints and four difficulty levels.
Try it on a live board