actually the pop cap is determined by the quality of the planet. It doesn't matter how many farms you build, the pop won't go above the cap thats determined by the planet quality. A formula was posted by someone from stardock that will figure out the exact number of pop that your planet will cap at.

Here you go:

Limit = 20 * ((Q+1)^3)

The food is per-planet, which seems kind of unfortunate. The pop-cap, as I've seen, depends on your food production. Colonies naturally start out with 5MT, and capitals with 10. There's apparently 1B people for 1MT of food, so it's not too hard to figure out.

That is, if I havn't gone completely looney.

PQ has nothing to do with PopCap. You can look at the planet screen and see how much food you are producing. To the right of that is a box showing planet population. Building run at the efficiency you set them at in your government window. It doesnt matter how many people you have. I have had a planet down to 5 million, yes million, people and still run the buildings at whatever efficiency I determinced from my tax and distro screen (f4). The only way to increase the pop cap is to build a farm. The farms produce varying amounts of food in megatons (mt) depending on your technology. Farms are a waste in the game. Dont build them unless you have a farming bonus square. The capital of your home world and the colony capitals produce enough food for 10billion, capital, and 5 billion, colony. Farms take up space for other more important spaces. They are only worth a wasted space if you get a bonus. Again, for those commenting you havent played the game. PQ has nothing to do with pop. and pop has nothing to do with efficiency.

Hope that helps the original poster. Sorry if you were confused by the others in here. The formula that the guy above is speaking of is a hard limit. No matter how many farms you build you cant go above it. You still have to build farms to get above the 5billion and 10billion limit. I am playing v1.D1.008