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Area of a Rectangle

In one line: The area of a rectangle is the amount of flat space inside it, and you find it by multiplying its length by its width.

Why it works

Area tells us how much surface something covers. You use it to work out how much carpet fits a floor, how much paint a wall needs or how big a garden bed is. Area is measured in square units. A square unit is a square with sides 1 unit long, such as a square centimetre (cm²) or a square metre (m²). Knowing the rule 'length × width' is also the first step towards finding the area of trickier shapes later on.

Think of it like: Imagine covering a rectangular floor with square tiles that are each 1 metre on every side. If one row holds 5 tiles and there are 3 rows, you have 3 × 5 = 15 tiles. The number of tiles is the area: 15 square metres. Multiplying rows by tiles in each row is a quick way to count every tile without counting them one by one. (Where this breaks: Real tiles have gaps between them and are hard to cut, but area has no gaps. Also, sides are not always whole numbers. A side of 2.5 m still works with length × width, even though you can't picture whole tiles. And the rows-times-columns idea only works on rectangles. Shapes like triangles or circles need other rules.)

Worked example

A rectangular photo is 8 cm long and 5 cm wide. What is its area?

  1. Check the shape is a rectangle: four straight sides and four square corners.
  2. Find the length and the width: length = 8 cm, width = 5 cm.
  3. Check both sides use the same unit. They are both in centimetres, so that's fine.
  4. Multiply length by width: 8 × 5 = 40.
  5. Write the answer in square units. Centimetres times centimetres gives square centimetres (cm²).

Answer: The area of the photo is 40 cm².

Common mistakes

  • Adding the length and width instead of multiplying them. Remember that area is rows × columns, so always multiply.
  • Mixing up area with perimeter (the distance all the way around the edge). Area is the space inside, found with length × width, not by adding up all four sides.
  • Leaving off the units or writing cm instead of cm². Area is always measured in square units, so write cm², m² and so on.
  • Multiplying sides that use different units, such as metres and centimetres. Change them to the same unit first, then multiply.

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A rectangle is 5 cm long and 3 cm wide. What is its area?

Questions parents ask

What year do kids learn the area of a rectangle?

In the US, children start finding area by counting squares and multiplying sides in Grade 3, then use the formula in Grade 4. In the UK, children count squares in Year 4 and calculate the area of rectangles in Year 5. In Australia, children compare areas using square units in Year 4 and solve area problems with metric units in Year 5.

What is the difference between area and perimeter?

Area is the space inside a shape, measured in square units like cm². Perimeter is the distance around the outside edge, measured in ordinary units like cm. For a 4 cm by 3 cm rectangle, the area is 12 cm² but the perimeter is 14 cm.

How can I help my child with area at home?

Draw rectangles on squared paper and let your child count the squares, then show how rows × columns gives the same answer much faster. Measure real objects together, such as a book, a table or a rug, and work out their areas. Always ask them to say the units, like 'square centimetres'.

Why is area written with a little 2, like cm²?

The small 2 means 'squared'. It shows that we multiplied centimetres by centimetres, so we are counting squares that are 1 cm on each side. It reminds children that area counts squares, not lengths.