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Mathematics & calculation

Area of a Rectangle Calculator (Square Feet or m²)

Calculate the area of a rectangle from its length and width: the floor area of a room, a wall, a lot or a sheet of paper. The formula A = L × W explained, sq ft, m² and cm² conversions, worked examples and common mistakes.

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Area

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How does this tool work?

This calculator multiplies length by width to give the area of a rectangle, in other words its surface. It is the basic calculation behind the square footage of a room, a wall to paint, a lot, a panel or a sheet of paper, and one of the first area formulas taught in school, along with the square.

The area of a rectangle is A = L × W: length times width. Picture it as a grid: a rectangle 4 m by 3 m holds 4 rows of 3 one-meter squares, so 12 m². A room 14 ft by 12 ft works the same way and holds 168 one-foot squares, or 168 sq ft.

Each dimension has its own unit selector, so there is nothing to convert beforehand: a length measured in meters and a width in centimeters can be entered as they are. Both values are converted before the multiplication, and the result is shown in the square of the first field's unit (m² if the length is in meters, ft² if it is in feet).

Area units do not convert like lengths: 1 m = 100 cm, but 1 m² = 100 × 100 = 10,000 cm². Likewise, 1 ft² = 144 in², 1 yd² = 9 ft², 1 hectare = 10,000 m² and 1 acre ≈ 4,047 m². This is the most common source of mistakes in homework and in material estimates.

For an L-shaped area or an irregular room, split it into several rectangles, calculate each area, then add them up; subtract a door, a window or an opening the same way. The formula assumes right angles: it does not apply to an arbitrary four-sided shape.

How to use this tool

  1. Enter the length

    Type the value and pick its unit; it sets the unit of the result.

  2. Enter the width

    It can be in a different unit: the conversion is automatic.

  3. Read the area

    The area appears in square units and updates on every change.

The formula for the area of a rectangle

A single multiplication, as long as both dimensions are in the same unit.

Area

A = L × l

Length times width.

Missing dimension

l = A ÷ L

Find one side from the area and the other side.

Area conversion

1 m² = 10,000 cm²

The length conversion factor is squared.

A
area, in square units
L
length
l
width (W)

Example: L = 6 m and W = 2.5 m, A = 6 × 2.5 = 15 m².

Use cases

Renovation and decorating

Work out the square footage of a floor, wall or ceiling to estimate the hardwood, tile, paint or wallpaper you need.

Real estate and land

Check the area of a room, a commercial space or a rectangular lot from its dimensions.

School and revision

Check an area exercise, a unit conversion or a figure made of several rectangles.

Fabrication and printing

Estimate the area of a panel, a tarp, a poster or a sheet for a per-square-foot or per-m² quote.

Examples

Bedroom floor area

14 × 12 = 168 ft² (about 15.6 m²), the starting point for ordering flooring; add 5 to 10% for waste.

Input

L = 14 ft, W = 12 ft

Result

A = 168 sq ft

Mixed units

80 cm = 0.8 m, so 2.4 × 0.8 = 1.92 m².

Input

L = 2.4 m, W = 80 cm

Result

A = 1.92 m²

A4 sheet

That is 0.06237 m²; sixteen A4 sheets make almost exactly one square meter (the A0 size).

Input

L = 29.7 cm, W = 21 cm

Result

A = 623.7 cm²

Plot of land

1,000 m² = 0.1 hectare, or about a quarter of an acre (0.247 acre).

Input

L = 40 m, W = 25 m

Result

A = 1,000 m²

Wall to paint

12.5 m² − 1.89 m² = 10.61 m² to paint, to be multiplied by the number of coats.

Input

wall 5 m × 2.5 m, door 0.9 m × 2.1 m

Result

≈ 10.61 m²

Tips and best practices

  • Measure each side of a room at least twice: walls are rarely perfectly parallel.
  • To convert cm² to m², divide by 10,000, not by 100; to convert in² to ft², divide by 144.
  • Split L-shaped or U-shaped areas into simple rectangles, then add the areas together.
  • Add 5 to 10% for cutting waste (15% for a diagonal layout).
  • Do not confuse area and perimeter: area is for the floor covering, perimeter is for the baseboards.

Sources and references

Frequently asked questions

What is the formula for the area of a rectangle?

A = L × W, the length times the width, both in the same unit. The result is in square units: cm², m², ft², km²...

How do I calculate the square footage of a room?

Measure the length and width of the floor in feet, then multiply them: a 15 ft × 12 ft room is 180 sq ft. For an L-shaped room, split it into two rectangles and add their areas. The same method in meters gives square meters.

How do I convert cm² to m²?

Divide by 10,000, because a square meter is a square 100 cm by 100 cm. For example, 9,600 cm² = 0.96 m².

How do I find the width if I know the area and the length?

Divide the area by the length: W = A ÷ L. A room of 18 m² that is 4.5 m long is 4 m wide.

Do two rectangles with the same perimeter have the same area?

No. A 6 × 4 m rectangle and a 9 × 1 m rectangle both have a 20 m perimeter, but their areas are 24 m² and 9 m². For a given perimeter, the square encloses the largest area.

Can I use meters and centimeters at the same time?

Yes. Each field has its own unit and the conversion happens before the calculation; the result follows the unit chosen for the length.

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