MENUCali Builds Areas – Area and Perimeter Game
Build shapes from squares on a grid and watch their area and perimeter change. In Explore you get a free board, or two boards to compare shapes. In the Game Cali has 6 levels of 6 challenges for you: build a shape with a given area, with a given area and perimeter, find the area of rectangles, L-shapes, triangles and trapezoids, and build shapes from squares of two colours. Your best stars are saved in this browser.
How to play
- Explore: fill squares on the board and watch the area and the perimeter change. Turn on “Two boards” to compare two shapes, for example two shapes with the same area and different perimeters. With “Hide numbers” you can guess first and check afterwards.
- Building: tap an empty cell to fill it, or drag to fill several cells. Tap a square to remove it, or drag it to move it. You can also drag the 1 × 2, 1 × 3 and 2 × 2 pieces onto the board (the round arrow turns them) and rub squares out with the eraser. Undo takes back your last steps and Clear empties the board.
- The Game: Cali gives 6 challenges per level: build a shape with a given area, with a given area and perimeter, or with squares of two colours, or find the area of a drawn shape. A shape you build must be one piece with no holes. Press Check when you are ready.
- Points and stars: a right answer on the first try gives 2 points, on the second try 1 point. 11 or 12 points earn 3 stars, 8 to 10 points earn 2 stars. After the second wrong try you can look at a solution.
- The 6 levels: 1 Build an area · 2 Area and perimeter · 3 Find the area · 4 Harder shapes · 5 Two colours · 6 Colours and perimeter. Every level is open from the start.
- Switches: “Grid” shows or hides the grid lines. “Side lengths” outlines your shape and writes the length of every side.
- Keyboard: click the board, then use the arrow keys to move the frame, Space to fill or empty a cell, 1–4 to choose a colour, Delete to empty a cell, M to pick up a square and to put it down, R to turn a piece, G for the grid, L for the side lengths and Ctrl+Z to undo. In the “find the area” challenges type the digits and press Enter. Esc goes back.
- Units: the game measures in inches: 1 square = 1 square inch (sq in), 1 side of a square = 1 inch (in). The first square of the grid is marked “1 in”.
What the game teaches
Area and perimeter. The area of a shape is the number of unit squares that cover it. The perimeter is the length of its border.
Rectangles. A rectangle with sides a and b has area a × b and perimeter 2 × (a + b).
Same area, different perimeters. Shapes with the same area can have different perimeters: the more compact the shape, the smaller its perimeter.
Complex shapes. To find the area of a complex shape, split it into rectangles and triangles, or take a bigger rectangle and subtract the missing part. A right triangle is half of a rectangle.
Area of Squares and Rectangles