How to Play Triangles
If you ever passed a rainy afternoon joining dots on a sheet of paper, you already know most of this game. Triangles is the triangle form of dots and boxes. In the square version, players take turns drawing lines on a grid of dots and claim each box they close. In Triangles the dots are laid out in a big triangle instead, so the little shapes you close are triangles with three sides rather than boxes with four. The game is sometimes called "dots and triangles" or "eternal triangles". This page explains the rules exactly as our free online Triangles game plays them, with examples.
What You Need
- Two players.
- On paper: a sheet of paper and two pens or pencils, ideally of different colors. On this site the game draws the board for you.
- About five to fifteen minutes a game, depending on the size of the board.
The Board
The board is a big triangle made of dots. There is one dot at the top, two dots in the row below it, three in the next row, and so on. Every dot is the same distance from its neighbors, so any three dots that are all next to each other form a small triangle. Some of these small triangles point up, and the ones in between point down.
The usual board has 6 dots along each side. It holds 25 small triangles and 45 possible lines. Our game also offers a Small and a Large board:
| Board | Dots on each side | Small triangles | Lines | Can it tie? |
|---|---|---|---|---|
| Small | 5 | 16 | 30 | Yes (8 to 8) |
| Medium (usual) | 6 | 25 | 45 | No |
| Large | 7 | 36 | 63 | Yes (18 to 18) |
To draw a board on paper, start with the bottom row of six evenly spaced dots. Put five dots in the row above, each one halfway between two dots below, then four, three, two and one at the top.
Taking Turns
Decide who draws first. On our site the first player is blue and the second is orange, and you can choose in Settings whether you or the computer starts. Then take turns. On your turn you draw exactly one line:
- The line joins two dots that are side by side: along a row, or along one of the two slanting directions. You can't skip over a dot or draw a long line across several.
- A line that has already been drawn can't be drawn again.
- You may not pass. Every line will be drawn by somebody before the game ends.
It doesn't matter who drew a line. Lines don't belong to anyone; only the triangles do.
Closing and Claiming a Triangle
Every small triangle has three sides. When a player draws the third side of a triangle, they have closed it, and it is theirs. On paper you write your initial inside it. On this site it fills with your color and pattern (blue with dots, or orange with stripes) and gets your letter, such as Y for you and C for the computer.
It doesn't matter who drew the first two sides. A triangle belongs to whoever draws the last side, which is why the second side is the dangerous one: once a triangle has two sides, the next player can simply close it.
Closing two triangles with one line
A line on the edge of the board touches only one small triangle, but a line inside the board is shared by two triangles, one on each side. If both of those triangles already have their other two sides, that single line closes both at once, and you claim both.
Going Again
Here is the rule that makes the game exciting: when your line closes a triangle, you must draw another line. It doesn't matter whether you closed one triangle or two; you get one more line. If that line closes a triangle too, you draw again, and so on. Your turn only ends when you draw a line that closes nothing (or when the board is full).
This is how big swings happen. A row of triangles that each have two sides can be closed one after another, like falling dominoes, all in a single turn.
House rule: some families play that closing a triangle does not give another line; turns simply alternate. You can switch that on in our game's Settings. Read more on the variations page.
Winning
The game ends when every line has been drawn. By then every small triangle has been closed by someone. Count them up: the player with more triangles wins. On the usual board there are 25 triangles, an odd number, so there is always a winner. On the Small and Large boards the count is even, so a tie is possible.
Worked Examples
Example 1: a safe line and a careless one. Early in the game, Ann draws a line on the left edge of the board. The triangle beside it now has one side. Ben draws a line in the middle of the board, touching two triangles that had no sides yet; each now has one. Both lines are "safe": neither gives the other player a triangle to close. Then Ann draws the bottom side of the triangle on the left edge. That triangle now has two sides, and Ben closes it with the third. Ben claims it and must draw again.
Example 2: a run of triangles. Later on, a row of four triangles along the bottom of the board each have one open side, and each open side is shared with the next triangle in the row. Ben is forced to draw a line at the end of that row. Ann closes the first triangle, which leaves the second with two sides, so she closes that too, and so on along the row. In one turn she takes all four triangles. Then, because her last line closed a triangle, she still has to draw one more line somewhere else.
Example 3: two at once. Two triangles share a side in the middle of the board. Each of them already has its other two sides drawn, so both are waiting for that same shared line. Whoever draws it closes both triangles at once, scores two, and draws again.
The Rules at a Glance
| Situation | What happens |
|---|---|
| Your line closes no triangle | Your turn ends |
| Your line closes one triangle | You claim it (1 point) and draw another line |
| Your line closes two triangles | You claim both (2 points) and draw another line |
| House rule "no extra move" is on | You still claim what you close, but your turn ends |
| Every line is drawn | The game ends: the most triangles wins |
| Equal number of triangles (Small or Large board) | A tie |
Common Questions About the Rules
Do I have to close a triangle if I can?
No. You may draw any line you like. But leaving a triangle with two sides for your opponent is nearly always a gift, so close it unless you have a very good reason. (There is one: see "leaving the last two" in our strategy guide.)
Does it matter who drew the lines around a triangle?
No. Only the player who draws the last side claims the triangle.
Can I draw a line from one corner of the big triangle to another?
No. Every line joins two neighboring dots, so each line is the side of one or two small triangles.
What if my extra line can't close anything?
You still have to draw it. Often that's the hard part: after a long run of triangles, your extra line may have to give something back.
Once you know the rules, the Triangles strategy guide explains safe lines, chains and the clever trick of leaving two triangles behind. For more games of pure skill with nothing hidden, try checkers or Reversi, or browse our puzzles.