It’s not obvious how many workers you need for each building. I’ve done the research so you don’t have to!
Farms and Pastures
Farms and Pastures are the only two buildings that don’t have an obvious scaling system.
For Pastures, only worker is really required. One worker can kill excess livestock, and there is never really a situation where the one worker can’t keep up with the number of livestock. This is especially useful early game, where labourers are at a premium. Additional workers will harvest more byproducts (dung, feathers etc) however.
For Farms, the variable here is the amount of time needed for harvest before winter. For my games, I use 8×8 farm plots. For an 8×8, only one worker is needed to harvest everything before winter. in an 8×16, for example, you’d need two workers. If you have plenty of spare labourers, then farms can benefit from more workers, as the time needed for planting and harvesting is reduced, resulting in more output. However I have found that this gain is marginal, and not worth using up excess labourers.
If you have randomly-sized farms, then just keep an eye on the farms once the “time to harvest” warning comes up. Start with one worker (or your best guess) and see if everything gets harvested before plants start to die. If you see any plants dying, then up the workers by one.
Finally, there is the ‘farming efficiency’ research, which boosts harvest and planting time by 100%. This is roughly equivalent to adding an extra farmer, so when this is researched, you can reduce the number of farmers by 1.
The marketplace is very difficult to find tangible benefits, but it is my belief that more workers here increases production elsewhere. Especially with the delivery technology, increasing the workers in the marketplace means workers elsewhere can work more efficiently because they themselves don’t have to visit the marketplace as often.
I personally use the marketplace as a spare labourer dump. Early game, if i have spare labourers, I chuck them in the marketplace. If i have a labourer deficit, then I’ll take them off and use them elsewhere. I slowly scale up the number of ‘permanent’ workers as my population grows, with the maximum 8 workers being used when the marketplace is at or near house capacity.
Processing Buildings (Basically Everything Else)
For most other buildings, the output scales linearly with the number of workers. For example, I tested forester’s hut and gatherer’s hut with different amounts of workers, and I found that the output increased roughly by 100% with each worker (depending on trees, worker distance, bunch of other variables, you could often see increases of 120%-130%, but likewise could see only 80-90% increase if the variables aren’t in your favour).
So for most other buildings, you scale the amount of workers based on the output you require. If you need more soap for example, then add more workers.
Note: I have not tested if it is better to have, for example, 2 buildings with 1 worker or 2 workers in one building, but my research would suggest that it would be the same. If anyone has any knowledge here, let me know and I’ll add it