Rectangular Prism Calculator

A rectangular prism, also called a cuboid or box, is a solid with six rectangular faces that meet at right angles. A cube is the special case where all three edges are equal.

Volume equals length times width times height. For a box of 3 by 4 by 5 that is 3 times 4 times 5, which gives 60 cubic units.

Surface area equals two times the sum of length times width, length times height, and width times height. For 3 by 4 by 5 that is 2 times (12 + 15 + 20), which is 94 square units, covering all six faces.

The space diagonal is the straight line from one corner to the opposite corner through the interior of the box. It equals the square root of length squared plus width squared plus height squared, so a 3 by 4 by 5 box has a diagonal of about 7.071068.

Yes. Set length, width and height to the same value and you get the cube results. A cube with side 2 returns a volume of 8, a surface area of 24 and a diagonal of about 3.464102.

It is unit-agnostic and just works with the numbers you type. If your sides are in centimeters, the volume is in cubic centimeters and the surface area in square centimeters; the diagonal comes out in the same linear unit as the sides.

Yes, the fields accept decimals and step in tenths. Each result is rounded to at most six decimal places for display, which is why an irrational diagonal like the square root of 50 shows as 7.071068.

The calculator requires every side to be greater than zero. A zero, blank or negative value produces a short message that the dimension must be positive, since a real box cannot have a side of zero length.

No. All three formulas run locally in your browser, so the dimensions you type stay on your device and the tool continues to work with no connection.