Key takeaways
- The area of a rectangle is A = l × w, length times width.
- Length and width must be in the same unit before you multiply.
- Area is always in square units, like m² or ft².
- Many different rectangles can share the exact same area.
In this guide
What is the area of a rectangle?
A rectangle is a four-sided shape where opposite sides are equal and every corner is a right angle (90°). Area is the amount of flat space inside it, like the floor space of a room. Multiply the two side lengths and you're done.
Why does the area of a rectangle matter?
Anyone buying flooring, carpet, paint, or turf needs to know exactly how much surface they're covering. Order too little and the job stalls; order too much and you waste money.
It can also fool you. Two rectangles can look completely different and still cover the same ground.
A 6 m × 4 m room, an 8 m × 3 m room, and a 12 m × 2 m room all cover exactly 24 m² of floor, even though one is almost square and another is a long, narrow strip.
The formula
| Symbol | What it means | Example |
|---|---|---|
| A | The area you want to find | 24 m² |
| l | The length of the rectangle | 6 m |
| w | The width of the rectangle | 4 m |
The formula is a straight multiplication: no squaring, no roots, just l × w.
How to find the area step by step
- 1Measure the length. Note the longer side of the rectangle.
- 2Measure the width. Note the shorter side of the rectangle.
- 3Check your units match. Convert one side if it's in a different unit from the other.
- 4Multiply length by width. This gives you the area.
- 5Add square units. Write m², ft², or whatever unit you measured in, squared.
Try changing the length and width in the calculator below to see the area update instantly, with every step shown.
Try it yourself
Pre-filled with the example — change any value.
Common mistakes to avoid
- Mixing units. Multiplying a length in meters by a width in centimeters gives a meaningless answer. Convert first.
- Forgetting the square symbol. Area is always written in units², like cm² or in², never plain cm or in.
- Assuming it must be a perfect rectangle. If all four sides are equal, you actually have a square, a special case of this formula.
Tips and tricks
- To compare two differently shaped rooms fairly, always compute area, not just "how big it looks."
- For the fencing or trim around the edge instead of the floor space, use the perimeter of a rectangle calculator.
- If you only know one side and the diagonal, find the missing side first with the diagonal of a rectangle calculator.
Where you'll use it in real life
- Home renovation: ordering flooring, carpet, or tile for a rectangular room.
- Gardening: working out turf or mulch for a rectangular lawn or bed.
- Painting: estimating paint coverage for a rectangular wall.
- Shopping: comparing the actual size of two rectangular items, like posters or rugs, that are labeled with different dimensions.
Quick summary
To find the area of a rectangle, multiply the length by the width and label the answer in square units. Keep both measurements in the same unit before you multiply. Use the calculator above to check your own numbers with every step shown.
Worked example
You're buying laminate flooring for a rectangular bedroom that measures 6 meters long and 4 meters wide. How many square meters of flooring do you need to order?
- 01A = l × w
- 02A = 6 × 4
- 03A = 24 m²
These numbers are pre-filled in the calculator above.
Frequently asked questions
How do I find the area of a rectangle without a ruler?
You still need two measurements — length and width — from some source, whether it's a tape measure, a floor plan, or a known package size. Then multiply them.
What's the difference between area and perimeter of a rectangle?
Area (l × w) is the space inside, in square units. Perimeter (2(l + w)) is the distance around the outside edge, in regular units like meters or feet.
Does it matter which side I call length and which I call width?
No. Multiplication gives the same result either way, so a 12 × 8 rectangle and an 8 × 12 rectangle have the same area.
How do I find the area of a rectangle if I only know the diagonal?
You need one more piece of information, such as one side, since many rectangles share the same diagonal. Use the [diagonal of a rectangle calculator](/calculator/diagonal-rectangle) alongside the Pythagorean theorem to find the missing side first.
