Rectangle Area Calculator
The area of a rectangle is its length times its width: area = l × w. Type a length of 12 and a width of 8 and the answer is 96, with the working printed under it as 12 × 8 = 96, so you can check the arithmetic yourself. This page opens on the rectangle, with the shape drawn beside the answer and its two sides labelled with the numbers you typed. Both sides go in one unit, millimetres, centimetres, metres, inches or feet, the area comes back in that unit squared, and the rows underneath give the same area in six more units, so a room measured in feet still reads in square metres.
Rectangle · l × w9,600 mm² · 0.0096 m² · 14.88 in²
Length times width. Any two sides that meet at a corner.
The formula is on the stage, and the working is the first row. Every answer here is one textbook formula with your numbers put in, printed so you can check it: a circle is π r², a three-sided triangle is Heron's formula, a regular polygon is n s² / (4 tan(π/n)). The solids give surface area for a closed shape, both ends of a cylinder and the base of a cone included. Conversions use exact definitions, so a square foot is 0.09290304 m² and 43,560 of them make an acre.
Common questions
- What is the formula for the area of a rectangle?
- Area = l × w, the length multiplied by the width. The formula sits on the stage beside the answer, and the first row under it is that formula with your numbers in place, for example 12 × 8 = 96. Both sides have to be in the same unit, and the answer is in that unit squared: 12 cm by 8 cm is 96 cm². The headline is shown to six significant figures and the rows below it to twelve, so a whole answer like 96 prints as 96.
- How do I get the area of a room in square feet or square metres?
- Pick the unit you measured in from the unit row, and the area comes back in that unit squared. A room of 12 ft by 10 ft is 120 ft², and the rows under the answer convert that same area into six more units, including 11.1483648 m², 13.3333333333 yd² and 17,280 in². The conversions use exact definitions: a square foot is exactly 0.09290304 square metres. If you measured in feet and inches, turn the inches into a decimal first, so 10 ft 6 in goes in as 10.5.
- Is a square just a rectangle with equal sides?
- Yes, and either route gives the same number here. Put 8 in both fields and the rectangle prints 8 × 8 = 64, while the Square button in the flat row takes a single side and prints 8² = 64 for the same shape. Use the square when there is only one number to type, and the rectangle when the two sides differ.
- Does this page give the perimeter too?
- No. It computes area only, which is the space inside the outline: l × w. The perimeter is the distance around the edge, 2 × (length + width), so the same 12 by 8 rectangle has a perimeter of 40 in whatever unit the sides were typed in. That is one addition and one doubling you can do on the numbers already in the fields.
- Why is my number rejected, and what can I type?
- The fields take plain numbers, with decimals and with thousands commas, so 10.5 and 1,200 are both fine while a fraction like 10 1/2 is not. An empty field says "Length is empty: type a number, like 5." A zero or a negative side says "Length must be greater than 0." Anything that is not a number says "Width needs a number, like 5: "eight" is not one." The message sits under the fields and names the field to fix.
- How do I handle an L-shaped room or a wall with a doorway?
- Split it into rectangles, work out each one here, and add them, or subtract the doorway rectangle from the wall. For a floor made of several rooms, the square footage calculator beside this one adds each room as its own line and totals them, with an L-shape among its shapes.
- Will it still open as a rectangle after I try another shape?
- Yes. This page always opens on the rectangle, even if the last shape you used on the main area calculator was a circle. The unit you chose and the numbers you last typed do come back, so the sides are yours and the shape is this page's.
Every area is computed from the formula shown, exact to the precision of the numbers you type, and conversions use exact unit definitions. Measurements from the real world carry their own error.