How to Play Dominosa

Dominosa was invented by O. S. Adler in 1874: lay out a full set of dominoes face up, copy the numbers, and let someone else work out where the borders were.

The rules

The grid holds every domino from 0-0 to n-n exactly once; only the numbers are shown.
Join pairs of neighbouring squares (side by side or one above the other) into dominoes.
Every square belongs to exactly one domino, and no two dominoes show the same pair.

Playing on kawu

Tap the gap between two numbers to make them a domino; tap again for a cross (not a domino); again to clear.
A domino that duplicates another is drawn dashed in red. The list under the grid shows which dominoes are still to place.
Undo steps back; Hint fixes a wrong join or adds a correct one.
Sets 0–3, 0–5 and 0–6; the daily puzzle is a 0–5 shared by everyone.

Next, read the Dominosa solving tips.

Frequently asked questions

How many dominoes are in the grid?

The full set for the highest number: 10 for 0–3, 21 for 0–5, 28 for 0–6. The grid is (n+1) rows by (n+2) columns, so it holds exactly that many.

Can the same pair appear twice?

No. Each domino, such as 2-5, appears exactly once. That constraint is what makes the tiling unique.

Last updated 2026-10-20