City growth mechanic

[ggmoyang]

Base value of growth is 2% of city population. In this case, 624 * 2% = 12.48 and rounded up to 12.5.
Then flat modifiers are added. I'm getting +10 from being a small city and +25 from the Feast amenity. We get total of 47.5
And then, this value is rounded. So we get 'surplus' of +0.5 to make it 48. You get waste when the number is rounded down.
Finally, percentage modifiers are applied. In this case I'm getting -10% penalty from low health. The final growth value is 48 - 4.8 = 43.2.
When the number of population reaches certain threshold the city tier goes up, providing various benefits.

Cities with tier 1~5 have +10 growth bonus, 6~10 have +5, and 11+ have -25% penalty.

Example of a big city.
Base growth value = 2066986 * 0.02 = 41339.72 -> 41339.7
City tier penalty is 25% that value, which is 41339.7 / 4 = 10334.925 -> 10334.9. We get 41339.7 - 10334.9 = 31004.8
Add up flat bonuses, then we get 31154.8. Then apply rounding. But here rounding is bit weird, I'm getting -49.8 waste. Anyways, 31154.8 - 49.8 = 31105, and that's the base number where percentage modifiers are applied.
+100% from health so +31.1k. Farms add +3% to growth, and 31105 * 0.03 = 933.15.

 

[Takfloyd]

So growth really has nothing to do with food directly(despite the tooltip stating it does), except that if there is a food deficit in the city, it doesn't grow and the global food stockpile, if any, is used to keep it from starving.