Geometry GlanceSources

Rectangle calculator

cm

cm

Advanced

Changing a measurement unit keeps its number: 3 cm becomes 3 m. Unit for all measurements applies to every input and the result. Result unit converts only the answers.

Four right angles. Both lengths must be positive.

Number format

Use a decimal point or comma, without thousands separators. Up to 15 significant digits and 64 characters; no fractions or expressions.

Rectangle schematic. Four right angles. Both lengths must be positive.LW

Not to scale

Enter your measurements to see the results.

No personal result is available. These are the rectangle formulas and conditions.

Formulas and conditions

Rectangle

A rectangle with adjacent length L and width W, joined at a marked right angle.LW
Area
A=LW
Perimeter
P=2(L+W)

L length · W width · A area · P perimeter

Four right angles. Length and width are positive.

Area uses square units; perimeter uses length units.

Diagrams are schematic, not to scale.

Length and width measure adjacent sides. Opposite sides are equal, so the boundary contains two lengths and two widths.

Area counts unit squares inside the rectangle. Perimeter measures the distance around its edge.

Use the same length unit throughout a formula. Convert mixed measurements first. Length and perimeter use units such as cm; area uses cm²; volume uses cm³. Decimal examples below are rounded to at most six significant figures, with ≈ marking an approximation.

Worked example: An 8 cm by 5 cm rectangle

  1. A = 8 × 5 = 40 cm².
  2. P = 2 × (8 + 5) = 26 cm.

An 8-by-5 grid contains 40 unit squares; adding the four sides gives 8 + 5 + 8 + 5 = 26 cm.

Formula sources

Formulas are checked against these references. The explanation, diagrams and worked calculations here are authored for Geometry Glance.