Rectangular Prism Calculator

About this calculator

A rectangular prism (also called a cuboid or rectangular box) is a three-dimensional solid with six rectangular faces, fully defined by its length, width, and height. From these three measurements, its volume is length × width × height, its surface area is the sum of all six face areas (2·(lw + lh + wh)), and its space diagonal — the straight line from one corner through the interior to the opposite corner — is found with a 3D extension of the Pythagorean theorem: √(l² + w² + h²).

This calculator computes all three from any length, width, and height you enter. It's a staple of geometry education for teaching 3D measurement concepts, and it's put to practical use in shipping and packaging for calculating box volume and material needs, in construction for room and material estimates, and in storage planning for figuring out whether an item will fit diagonally into a box or space.