Rectangular Prism Calculator
Calculate box volume, surface area and space diagonal from three perpendicular edge lengths.
What would you like to do next?
Calculate the capacity and exterior of a rectangular prism
Enter length, width and height to calculate volume, total surface area and the diagonal between opposite corners. The three outputs support storage, packaging and classroom geometry from one consistent set of dimensions. The space diagonal also offers a useful check when an object must fit inside a box even though its individual edge lengths appear acceptable.
Use internal or external dimensions deliberately
A real container has wall thickness, closures and unusable clearance that an ideal prism does not include. External dimensions describe occupied space, while internal dimensions better represent theoretical capacity. Use the same unit on all three edges, confirm that they meet at right angles, and apply packing efficiency or material allowances as separate constraints rather than altering the formula.
Frequently asked questions
How is the space diagonal calculated?
It is the square root of length squared plus width squared plus height squared.
Should I use internal or external dimensions?
Use internal dimensions for theoretical capacity and external dimensions for occupied space.
Does volume equal usable packing capacity?
Not always. Contents, clearance and packing efficiency can reduce usable capacity.