Rectangle - Length, Width, and Properties

A rectangle calculator turns the length and width of a rectangle into area, perimeter, diagonal, and aspect ratio in a single read. The default 10 by 6 meter rectangle returns 60 m², 32 m, 11.6619 m, a 1.7:1 aspect ratio, and a square-foot reference of about 645.83 ft².

• • Flooring and material takeoffs: Estimate square footage or square meters for a room, deck, garden bed, or accent wall before ordering flooring, paint, turf, or fabric.
• • Framing, trim, and fencing: Compute the perimeter of a rectangular frame, panel, or fence run so you can order moulding, baseboards, or edging in one continuous length.
• • Diagonal and aspect ratio for screens and panels: Get the diagonal for a TV, monitor, projector screen, or painter's bracing cut, with the aspect ratio reported at the same time.
• • Geometry homework and exam prep: Cross-check the area, perimeter, and diagonal of a textbook rectangle so you can compare your hand-written work to a known answer.

The result panel keeps every value in sync as you type, so the area, perimeter, diagonal, and aspect ratio are always consistent with the same length-and-width pair.

The rectangle calculator in the same cluster adds reverse solve modes for area-plus-side and perimeter-plus-side when the user knows one side and a total instead of two sides.

The calculator reads the length, width, and unit inputs and runs the three rectangle formulas plus a unit conversion. A unit selector switches the linear and square units so the same numbers describe a 10 by 6 meter room or a 10 by 6 foot panel without retyping.

• length: The rectangle's longer side. Drives the area, the perimeter, the diagonal, and the aspect ratio.
• width: The rectangle's shorter side. Drives the area, the perimeter, the diagonal, and the aspect ratio.
• unit: The linear unit for length and width. Meters report the area in m² and a square-foot reference. Feet report the area in ft² and a square-meter reference.

The diagonal uses the Pythagorean theorem on the right triangle formed by the two sides, so a square returns a diagonal that is the side length times the square root of two. The result panel keeps the area, perimeter, diagonal, and aspect ratio in lockstep, so changing the unit selector changes the linear and square units together.

According to Omni Calculator rectangle page, the area is length times width, the perimeter is 2 times the sum of length and width, and the diagonal is the square root of length squared plus width squared.

According to Wolfram MathWorld rectangle entry, Wolfram MathWorld defines a rectangle as a four-sided polygon with all right angles and lists the same area, perimeter, and Pythagorean-diagonal formulas used in this calculator.

When the user needs the angle the diagonal makes with the sides or the angle at the diagonal intersection, the rectangle diagonal angle in the same cluster returns the four distinct angles from the same length and width pair.

Four ideas explain every value the result panel shows.

These four rules cover every rectangle problem the calculator is designed for. The area is in the input square unit, the area reference is in the opposite square unit, so the same input pair covers both metric and imperial material lists.

A square is a rectangle whose length and width are equal, so when the rectangle is a perfect square, the square area calculator in the same cluster is the right tool for area, perimeter, diagonal, and side-length conversions on a square-only workflow.

Four short steps turn any length and width into the four rectangle properties plus the cross-system area reference.

1. 1 Pick meters or feet for the project: Use meters for metric projects so the area comes back in m² and the reference area in ft². Use feet for imperial projects so the area comes back in ft² and the reference area in m².
2. 2 Type the longer side into the length field: Enter the longer of the two visible sides. For a room, this is the longer wall. For a TV or monitor, this is the longer panel dimension.
3. 3 Type the shorter side into the width field: Enter the shorter of the two visible sides. For a room, this is the shorter wall. For a TV or monitor, this is the shorter panel dimension.
4. 4 Read the four properties plus the area reference: The result panel reports area, perimeter, diagonal, aspect ratio, and a reference area in the opposite square unit. Use the area for material takeoffs, the perimeter for ordering trim, and the diagonal for layout cuts.

You are planning a 4.2 by 3.0 meter deck. Type 4.2 in length and 3 in width, and the panel returns area 12.6 m², perimeter 14.4 m, diagonal 5.1589 m, aspect ratio 1.4:1, and a reference area of about 135.6253 ft².

If the user only has an area and a perimeter and needs to recover both side lengths at once, the length width area rectangle calculator in the same cluster solves the area-plus-perimeter pair so the two inputs can be recovered together.

A rectangle calculator saves time and removes the unit-conversion mistakes that come from doing the four properties by hand.

• • Four results from one input pair: Length and width produce area, perimeter, diagonal, and aspect ratio at the same time, so the user does not need four separate calculations or four separate calculators.
• • Cross-system area reference for material lists: The reference area row converts the rectangle into the opposite square unit (m² to ft² or ft² to m²), so the same result is usable on a metric and an imperial material list without a separate conversion step.
• • Aspect ratio for screen, photo, and panel sizing: The length-to-width ratio is reported alongside the other outputs, which is useful for screen sizing, photo cropping, and floor plan labels where the user needs to know the shape of the rectangle without naming the side lengths.
• • Real-time recalculation as you type: Every change to the length, width, or unit fields updates the result panel immediately, which is helpful when the user is comparing rectangles or trying out a target ratio.

When the user needs to scale a known rectangle to a new size, the same length-and-width pair feeds a scale factor step, and the aspect ratio and the property relationships carry through unchanged.

When the user needs to scale the same rectangle to a new size, the rectangle scale factor in the same cluster takes the original and the target rectangle and returns the linear scale factor, the area scale factor, and any missing side.

Three variables drive the result and two limits tell you when the geometry stops being a clean rectangle.

• • The calculator assumes the four corners are right angles. A parallelogram with non-right angles has the same area formula, but a different perimeter and a different diagonal, so the formulas do not transfer.
• • Negative inputs are clamped to 0, so a width of -3 is treated as 0 and the rectangle collapses to a line segment with area 0, perimeter equal to twice the length, and a diagonal equal to the length.

For the cross-system area reference, this calculator uses the international foot of 0.3048 meters, published by NIST, so the same input pair produces a metric area in m² and a square-foot reference, or an imperial area in ft² and a square-meter reference.

According to NIST Guide for the Use of the International System of Units (SI), one international foot is exactly 0.3048 meters, which is the factor this calculator uses when it shows a reference area in the opposite unit family.

If the rectangle is a face of a three-dimensional box, the surface area of a rectangle calculator in the same cluster extends the length-and-width pair into the full surface area of a rectangular prism.