That depends on what you mean by "calculate". There are 12 of them but their lengths depend on having a lot more information.
A rectangular prism can have 12 edges, but not every shape with 12 edges is a rectangular prism.
A rectangular Prism has 12 edges.
The rectangular prism has 12 edges.
A rectangular prism has 12 edges.
There are twelve edges in a rectangular prism.
A rectangular prism has 12 edges and 8 vertices.
There are 12 edges and 8 corners in a rectangular prism
A rectangular prism has 12 edges.
actually all edges of a rectangular prism are parallel to another edge
A rectangular prism.
12 edges
A rectangular prism has 12 edges and 8 vertices.