How to find area

Area is the amount of space inside a flat shape, measured in square units. For a rectangle, multiply length × width: a 6 cm by 4 cm rectangle has an area of 24 cm². This page shows why by counting squares, covers L-shaped areas and triangles, has a rectangle builder, and explains the area–perimeter mix-up.

Area: the big idea

Area counts how many unit squares cover a shape. Counting one by one is slow, so we count rows: a rectangle with 4 rows of 6 squares has 4 × 6 = 24 squares. That is why area = length × width.

How to find the area of a rectangle

1. Measure the length and width in the same unit.
2. Multiply length × width.
3. Write square units: cm², m², in², ft² or “square units”.

For a square, all sides are equal: side × side. A 5 m square has an area of 25 m².

Area of L-shapes and other composite shapes

Split the shape into rectangles, find each area, and add. An L-shaped room made of a 6 × 4 m part and a 3 × 2 m part has an area of 24 + 6 = 30 m² (3.MD.C.7d). Or find the big rectangle around it and subtract the missing corner.

Area of triangles and other shapes (grade 6)

• Triangle: ½ × base × height. A triangle is half of a rectangle.
• Parallelogram: base × height (cut off a triangle and move it to make a rectangle).
• Circle (grade 7): π × radius².

Common mistakes

How to teach it at home

Tile counting

Count floor tiles in a room, then check with rows × columns.

Plan a rug

Measure a room and work out the area of rug it needs.

Graph paper rooms

Draw a dream bedroom on graph paper and find its area.

By grade

• Grade 3 (3.MD.C.5 to 3.MD.C.7): area by counting squares, then multiplying; composite rectangles.
• Grade 4 (4.MD.A.3): area formula in real problems.
• Grade 6 (6.G.A.1): area of triangles and polygons.
• See also perimeter and volume.

Worksheets and practice

Area of rectangles worksheet: printable PDF with an answer key. · Make a fresh test

Area of triangles worksheet · Perimeter and area chart