If you bring up the Economics window (F2) and select the Wealth/Trade tab, you will see an estimate for the production and consumption of commercial goods at the colony you have selected. Recall that these numbers reflect the expected Annual production, not production from a single build cycle. In order to haul goods, civilian ships need goods to be physically present in the first place.
If commercial goods are present, but are going unhauled, you need to encourage more shipping to occur between build cycles, so that more tons of goods are hauled per build cycle. Specifically, you need to allow your civilian ships to run out of commercial hauling contracts on Earth, which will force them to begin servicing other colonies. At present, civilian shipping only handles a single trade run per explicit time increment. This means that when you run a single 30 day increment, all of your civilian shipping attempts a single trade run. If you run a single 5 day increment, all of your civilian shipping attempts a single trade run. If you run a series of 8-hour time increments, all of your shipping will always attempt to be busy hauling goods, as opportunities arise.
If you pursue this avenue, you would do well to learn exactly how the Auto-Turns feature works. It helps me immensely. Using 8-hour intervals and Auto-Turns, and periodically setting Mars as a source of colonists and Earth as a destination, until Mars runs low on people, means that I get more in taxes on shipping colonists then I do from taxes on populations. Good times.
I do not recall the calculations involved in establishing new Civilian Mining Colonies.
