How to calculate rectangle area
Area = length × width. Use consistent length units; the result is in square units. For example, measurements in metres produce square metres (m²). Enter the measured dimensions, select the matching method and choose Calculate area.
Practical questions
How much flooring do I need for a rectangular room?
For a room 8 m long and 5 m wide, enter 8 and 5 to get 40 m². This is the floor area before any allowance for cutting or spare material. Subtract separately measured areas that will not be covered.
Can I use this to measure a wall?
Yes. Enter wall width and height in the same unit. Subtract the areas of doors or windows separately if they will not be covered.
What if my room is not a rectangle?
Divide it into rectangles, calculate each area, then add them. Subtract cutouts and avoid counting overlapping parts twice.
Is perimeter the same as area?
No. Area measures the surface inside the rectangle in square units. Perimeter measures the boundary length in ordinary units.
How do I subtract a window from a wall before decorating?
For a wall 5 m wide and 3 m high, calculate 15 m². A window 1.5 m wide and 1.2 m high has an area of 1.8 m². Subtract the window to get 13.2 m² of wall surface. Subtract any other uncovered openings separately. Paint coverage and the number of coats are separate calculations.
How can I estimate a material cost from a price per square metre?
Multiply the area by the price per square metre. A rectangular surface measuring 8 m by 5 m has an area of 40 m². At $25 per m², the area-based material cost is $1,000. Delivery, installation, cutting allowance and other charges are not included in that multiplication.
How do I calculate a rectangular border around a garden bed?
Calculate the outer rectangle and subtract the inner one. For a 5 m by 3 m bed with a 0.5 m border on every side, the outer dimensions are 6 m by 4 m. The border area is 24 − 15 = 9 m². Add twice the border width to each inner dimension.
Can I estimate how much fencing I need?
Use the perimeter result. A plot 12 m long and 8 m wide has a perimeter of 40 m. If a 2 m opening needs no fencing, subtract it to get 38 m of fenced boundary. Posts, corners, gate fittings and panel widths must be planned separately.
How should I enter measurements taken in metres and centimetres?
Convert them to one unit first. For example, 2 m 40 cm is 2.4 m, not 2.40 cm or 2.04 m. A rectangle 2.4 m by 1.5 m has an area of 3.6 m². Changing the unit selector only relabels your entries; it does not convert them.
Does the diagonal help me check whether a frame is square?
The calculated diagonal is the corner-to-corner distance expected for a rectangle with your entered sides. For sides of 3 m and 4 m, it is 5 m. Comparing measured diagonals can help spot a distorted frame, but equal diagonals alone do not prove that an arbitrary four-sided shape is a rectangle.