Yes, but in most cases you can default to a constant like 5 in. Package dimensions are only used in special cases. For example, UPS might charge you a small fee for shipping a fish pole even though it might have the same weight as a small package. This is because a fishing pole can be difficult to transport and takes up more space. This ratio of space to weight is often referred to as dimensional weight.
Most shippers can just set all packages to specified dimension without an effect on the accuracy of rate; however, if you suspect that you will be shipping irregular or oversized packages experiment with providing the actual package dimensions and see if the rate changes.
For certain carriers, such as UPS, you can supply us with the dimensions. However, for most carriers, volumetric weight cannot be done through our automisation.
If you have any further questions, please get into contact with our support team.