Rectangular Box (Cuboid) Calculator

A cuboid, also called a rectangular prism or rectangular box, is a three-dimensional shape with six rectangular faces where opposite faces are equal. It is the most common shape in everyday objects: boxes, rooms, bricks, books, and crates are all cuboids. Unlike a cube, a cuboid can have three different dimensions: length, width, and height. This calculator takes those three measurements and returns the volume, the total surface area, and the space diagonal. Volume tells you the capacity of the box and is used in shipping, storage, and fluid calculations. Surface area tells you how much material you need to cover the outside, which is relevant for wrapping, painting, or insulating. The space diagonal is the longest straight line that fits inside the box, running from one corner to the opposite corner through the interior, and it determines whether a long object such as a pipe or a rod will fit inside. Enter length, width, and height in any consistent unit and the calculator returns results instantly. All dimensions must be positive. The result labels say cubic units and square units, so just substitute the unit you used. For example, if your dimensions are in centimetres, volume will be in cubic centimetres and surface area in square centimetres. Use the tool for homework, packing calculations, or any practical sizing problem where you need all three measurements at once.

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