Trade Routes

The basic Formula for the value of a Trade route seems to be

[(1+F)*(5*(Pop-10))+100+Cap)* (Minimum ([T*50%], [D*70%]))*20%/100]
  • F is 150% (1.5) if it is a Foreign Trade Route, 0 if domestic
  • Pop is the Pop of the city Getting the trade route
  • T is the Pop of the City the Trade Route is With
  • D is the Distance to the City
  • Cap is 25 if one of the cities is conected to the Capital, 0 if not
  • [] indicates rounding down

This is for Overland routes, no Harbors, Tiny map

The 69% for distance is Probably specific to Tiny maps

All the numbers (150% for Foreign, 5* population, -10 population adjustment, 25 for Capital, 50% for partner pop, etc. except the 1 and the 100 are in the XML files)

What this indicates is that on a normal map, once your empire is big enough, and the populations are about 20, then Domestic trade routes can make about 3 commerce, 2 quite easily. Foreign Trade Routes can get to 7 or 8 and don’t require your empire to be big just to have sufficiently Distant and large-citied trade Partners.

Checked World info for the other sizes too,

So for
Duel is 80%
Tiny 70% (I discovered I made a distance measuring mistake in my 69% calc, Credit to Roland: I would have missed that)
Small 60%
Standard 50%
Large 40%
Huge 30%

Editing for BTS:
BTS explains it a lot better in that there are 2 components to trade
1.= Base value
Base Vaue is the SMALLER of
Population of Other city/10
Distance to the other City * 15%->40% (Huge->Duel)
but Base Value has a Minimum possible value of 1

2. Modifiers, these are all +% and are added together and then the total is used to modify the base value.
Then the Base Values have % modifiers added, the % modifiers are
+5% for population of the Receiving city over 10
+25% if the receiving city has a connection to the Capital
+3% per turn since your last war with the civ (if it is another civ) [max 150%]
+50% if you have a Harbor
+100% for the ToArtemis
+100% if the other city is on another continent
+100% if it is another civ on another continent AND you have a Customs House

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