Condition for Dimension

This is a feature request, not a bug report. Here is a patch to play around with.

Domestic shipments are generally flat rate shipping or calculated by physical weight.

For international packages and couriers such as Fedex/UPS/DHL , there is also calculation by dimensional weight.
I.e. USPS calculates by L"xW"xH"/166=dimensional weight

An example of how dimensional weight may be useful.

A product that is large in overall dimension and require a box that is 13"x10"x4"=3.13lb
But the product's actual physical weight is only 1lb and there are additional spaces in the box to fill and maximize the capacity.
If any additional small size item product is added it will add to the 3.13lb in shipping calculation.

Perhaps it would be helpful to have a check box option on whether a product can be combined shipped and what items could be combined?
And/Or some kind of rule to distinguish physical weight vs dimensional weight of a order prior to calulating shipping costs.

#6 worked