Area of a rectangle

What the symbols mean

$A$

the area, in square units (cm², m²)

$l$

the length

$w$

the width

When to use it

Use it for floors, walls, screens, fields and any other rectangular surface, and as the building block for other shapes: a parallelogram, a triangle and a trapezoid are all worked out from it. Measure both sides in the same unit first.

Why it works

A rectangle 8 units long and 5 units wide holds 5 rows of 8 unit squares, so 40 squares in all. The graph draws the squares. For lengths that are not whole numbers the same rule still holds.

Common mistakes

• Mixing units: 2 m by 50 cm is 2 × 0.5 = 1 m², not 100.
• Confusing area with perimeter. Area is $l\times w$ in square units; perimeter is $2(l+w)$ in plain units.
• Converting square units like plain units: 1 m² is 10,000 cm², not 100 cm².