What this calculator does
The area of a rectangle is the amount of flat space it covers, found by multiplying its length by its width. It is one of the first area formulas taught precisely because it needs nothing more than two straight measurements and a single multiplication.
This calculator leads with that area as the headline figure, taking a length and a width and returning the area of rectangle first, with the perimeter and diagonal given underneath for whichever secondary measurement the job also needs.
The formula
The area of rectangle formula is A = l × w, length multiplied by width. Both measurements need to be in the same unit; the resulting area comes out in that unit squared, so metres times metres gives square metres.
| Term | Meaning |
|---|---|
| l | Length: one side of the rectangle. |
| w | Width: the adjacent side, perpendicular to the length. |
| A | Area: the space enclosed by the rectangle, l × w. |
The inputs explained
| Field | What to enter |
|---|---|
| Length | The length of the rectangle. |
| Width | The width of the rectangle, the side adjacent to the length. |
When to use it
Costing flooring, turf or paint
Materials priced per square metre need the actual area of a rectangle, not either side length alone, before a per-unit price can be multiplied out into a total cost.
How to find the area of a rectangle for a school problem
A geometry question giving a length and width is solved directly here, with the perimeter and diagonal shown too in case the same problem asks for those as well.
Comparing two rectangle area formula results
Two rectangles with the same perimeter can have very different areas, so working out the actual rectangle area rather than assuming it from the perimeter avoids a common sizing mistake.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Area of rectangle formula across a range of lengths
A fixed width of 6, across a range of length values.
Area of a rectangle across a range of widths
A fixed length of 16, across a range of width values.
Questions
How do you find the area of a rectangle?
Multiply length by width. Both measurements need to be in the same unit, and the result comes out in that unit squared: metres times metres gives square metres.
What is the area of rectangle formula?
A = l × w, where l is the length and w is the width. It is the same formula regardless of which side is called length and which is called width.
Does the area of a rectangle change if you swap length and width?
No. Length times width gives the same answer as width times length, since multiplication does not depend on order. Only the perimeter and diagonal calculations are unaffected by which side is labelled which.
How is rectangle area different from perimeter?
Area measures the enclosed space, in square units, while perimeter measures the total distance around the edge, in linear units. Two rectangles can share the same perimeter yet have very different areas.
For perimeter, diagonal and aspect ratio all together, see the full rectangle & square calculator. For a three-dimensional version of the same shape, see the rectangular prism calculator.