How do you find out a volume for a irregular cube?

Answer 1

A cube is, by definition, regular.

Do you mean a cuboid? The volume of a cuboid is length × width × height or length × width × depth (where depth and height are the length in the third dimension).

For irregular three dimensional shapes, divide them up into smaller shapes for which the volume can be calculated and add them together.

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For real world irregular three dimensional object it is impractical to try to split the object up into smaller shapes. In this case get a cuboid of water (or other liquid) in a tank, measure its volume (as above), submerge the object completely in the liquid and re-measure the volume of the liquid (the tank should have excess capacity greater than the volume of the object so that no liquid spills): the volume of the object is the difference between the two measurements of the volume of liquid.

Answer 2

If an object is a cube, it's regular, not irregular.To find the object of arbitrary, irregular shapes, you divide the shape into lots of small pieces, for example cubes, calculate the volume of each piece, and add everything together. This is called "integration"; you can read about that if you want more details.