Single Position (Hidden Single)

Play Now

Single Position (Hidden Single)

What It Is

A single position (hidden single) is a number that can only go in one cell of a unit (row, column, or box), even if that cell shows other candidates. The digit is “hidden” as the sole spot in the unit.

When to Use

Use hidden singles after scanning and naked singles, mid-early game. If a unit is missing a digit and only one cell can take it, place it.

How to Find a Hidden Single (Step-by-Step)

  1. Choose a unit: pick an incomplete row, column, or box and list missing numbers.
  2. Check candidate positions: mark cells where each missing number could go.
  3. Isolate a sole cell: if a number fits only one cell in that unit, that’s the hidden single.
  4. Place the number: fill it in that unique cell.
  5. Update the grid: remove that number from peers and repeat elsewhere.

Hidden singles are the inverse of naked singles: you find a number with only one possible cell. Cross-hatching a single digit across a box can reveal the lone place it fits—spot it and place it confidently.

See also

Scanning / Cross-Hatching Single Candidate (Naked Single) Single Position (Hidden Single) Naked Pairs / Triples / Quads Hidden Pairs / Triples / Quads Pointing Pairs / Triples (Locked Candidates Type 1) Box–Line Reduction (Locked Candidates Type 2) X-Wing Swordfish Jellyfish XY-Wing XYZ-Wing W-Wing Alternating Inference Chains (AICs) Forcing Chains / Forcing Nets Nishio Coloring Multi-Coloring Uniqueness Techniques (Unique Rectangle etc.) Fish Variants (Finned X-Wing, Sashimi etc.) ALS Techniques (ALS-XZ, ALS Chains) Sue de Coq Pattern Overlay / Template Method
Ready to practise?
Try a fresh Sudoku puzzle now → /play