EPTI used to build as many drones as I can get away with. But when I hit B-, my opponents started to out macro me consistently. Several times I've been told by my opponents that I make too many drones, which was really confusing to me. But the idea is simple, if you make more workers than you need, eventually you end up having lots of excess minerals in the bank for no good purposes, but in the mean time you waste valuable resources and time making workers, and your army is smaller than it should be.
Recently, I played a good Korean zerg who later taught me the 9 pool build like I've never seen it before, and what amazed me was how calculated and exact his econ management was, perfect, not a single drone more than he needs, not a single drone less. That exactness of Koreans in their econ management is precisely why they can pump out so many more units. So, afterward I did an experiment with all zerg units and figured out the amount of income needed to maintain constant production of each unit. And I will put all my findings into this zerg econ guide to share it with others. Be reminded that my max rank was B- a couple seasons ago, so I'm not gosu or anything, just hope this helps.
How many drones do I need to maintain constant production of a ..... from 1 hatchery?
Drone: 3 drones mining minerals
Zergling: 3 drones mining minerals (duh, it costs 50 minerals just like the drone)
Overlord: this unit is unique since you don't constantly produce it....you just need to start a new one when the old one pops out. 2 drones per overlord is good, if later in the game you need to make 2 overlords every round, then 4 drones, no more will be needed, ever.
Hydralisk: 6 drones on minerals + 1 drone on gas ( remember, we are talking about 1 hathcery)
Mutalisk: 4 drones on minerals + 3 drones on gas. It should be noted that this combo gives you the same amount of minerals as gas, 100/100 for muta, and the same combo is used for lurker and ultralisk.
Note, in zvz for muta/ling combo, it's 6 drones on minerals + 3 drones on gas per hatchery, mainly because mutas are limited by gas, not larva, so you will have excess larva and no gas for the zergling.
Scourge: 1 drone on mineral + 3 drones on gas. This unit is only constantly produced in the ling/scourge strategy in zvz. And for that 3 drones on minerals + 3 drones on gas should maintain constant production of ling/scourge from 1 hatchery.
Queen: Omitted from experiment due to lack of use.
Lurker: 4 drones on minerals + 3 drones on gas. This includes the hydralisk cost.
Defiler: 3 drones on minerals + 3 drones on gas, you get a little excess minerals, but 2 drones on minerals is not enough.
Ultralisk: 4 drones on minerals + 3 drones on gas.
How to make use of this information strategically?
Nowadays every game looks like one you have seen many times before, and the reason is because the Korean exactness is taking over the game. Every build they use has a hidden econ side that not everyone notices, but if you look into it you will find that every build ultimately yields the exact amount of workers needed for the strategy of that build. I will do a complete build analysis later. But here let's consider some simple cases:
I want to do mass hydra so how many drones do I need?
Well, to maintain constantly production of hydras from 1 hatch, you need 6 drones on minerals + 1 drone on gas (see section above). So it really depends on how many hatches you want to have in your particular strategy.
If you are doing a 2 hatch hydra break, once the upgrades are done, you can take off a drone from the gas, and have 14 on minerals + 2 on gas. (6 per hatch for hydra + 2 for overlord) If you are doing a 5 hatch mass hydra, then you need 5*6+2=32 drones on minerals and 5 drones on gas. Calculating this way gets you the exact amount of drones you need, and then you can maximize your army size.
It's zvz and I never know when to make drones and when to make units?
Simple, if you want to do ling/scourge, multiply the amount of hatcheries you want by the drone combo, 3 drones on minerals + 3 on gas. So if you are doing 1 base ling/scourge with 2 hatcheries, you need 6 drones on minerals and 3 on gas.
If you have 3 hatcheries and 2 bases, and you want to do muta/ling, you will need 6+6+3=15 drones on minerals and 6 drones on gas. Where is the overlord? Well, due to the intense nature of zvz, you can always skip a couple of lings to make an overlord, the only thing that matters is the amount of mutas you have anyway. But if you think your opponent won't be aggressive and you want steady growth, by all means add 2 drones for that overlord.
The same calculation can be done for any unit combo. So, if you woke up one morning and a nice strategy comes to mind, you can now easily calculate how many drones you need to make that strategy happen!
Case Study - zvt 3 hatch muta build analysis
Let's first calculate how many drones you need for this strategy. We know that the muta contain is only a transition phase into lurker/ling, then when hive comes, you expo and add defiler into the army, and when you secure more gas, and your carapace up is looking good, switch to ultra/ling.
Too much depends on the actual game so we won't do this match up to the end game, but unless somethings goes horribly wrong with your muta harass, you should enter a 5 hatch lurker/ling phase without any problem. Since lurker production is limited by gas, not larva, with 3 gas you can keep 3 hatches producing lurkers, which equals to 4*3=12 drones on minerals + 3*3=9 drones on gas; now you have no more gas, but you want to keep 5 hatches pumping lings (again, lurker production will yield excess larva for the hatchery since it's limited only by gas), that means 3*5=15 additional drones. Don't forget the overlord, that's another 2 drones on minerals. Let's sum things up, we have 12+15+2=29 drones on minerals, plus the 9 drones on gas for a grand total of 38 drones. But wait! you want to expo again sometimes, right? Put another 3 drones on minerals to afford your 4th expo, and when the expo is up, add more drones depending on whatever strategy you want to use for the end game.
So, that is our analysis. Do the pros actually do that? Let's work through a typical 3 hatch muta build. (There are billions of pro replays out there that feature the exact same 3 hatch muta build, you can find a rep yourself...)
12 hatch
11 pool
14 hatch
16 gas
25 gas
Spire when lair finishes
33 hatch (note that if you made 3 sunkens you will not be able to afford this, cuz you spent it on 2 of your sunkens...)
Shoot up to 35 supply, then make 3 overlords. Overlords finish at the same time as your spire, and you should have 900/900 to pop the mutas, yeah yeah everyone knows...
Assume that you lost no units for the sake of easy calculation. After 11 mutas your supply should be at 35+22=57. Subtract the mutas and 12 zerglings you should have 29 drones, 6 of which are on gas, so 23 on minerals. Looking at our goal of 29 drones on minerals + 9 on gas, are we only 9 drones short? Not quite, remember that a drone is lost for every building you make. At this point we need a hydralisk den, an evolution chamber, another geyser, another hatchery, plus a queens nest, and in all likelihood another 2 sunkens, so that is 7 drones lost that we have to replace, plus the 9 we needed earlier for a total of 16 drones that you need to make.
Coming back to the build analysis, at 57 supply where we left off you are gonna use 6 drones on buildings (queen's nest is usually gotten at the same time as lurkers, so that's after you make your hydras), that puts your supply back to 51, and after making 13 drones while you are muta harassing, at 64 supply it is time to make hydras and go lurker/ling like we wanted. Later, you can add a 3 more drones to meet your production requirement, and make a few additional drones for more buildings and save money to expo again. In fact, a lot of progamers go to 68 supply before they make hydras, but understand that it requires gosu muta micro to contain the terran for your delayed lurkers, and I don't recommend it unless you are feeling good about your muta harass, much easier is to make lurkers first, and then add a few drones. The econ boost from a few earlier drones is significant at the pro level, but not to most of us.
OK, that concludes our zerg econ guide, I've given you the drones needed for each unit, walked you through some simple calculations so you can use the numbers for yourself, and I've analyzed the econ side of the popular 3 hatch muta build as a case study. The rest is up to you. I hope I can improve myself with this new insight, and I hope you guys can benefit from it as well. GGs
Bonus Terran Section:
This might look counter-intuitive, aren't you helping the zergs you might ask? Well, I'm trying to help the whole community, it's just that I play zerg and I'm not familiar with the other races' econ management. But I've done some work on the Terrans as well.
Marine: 3 scvs on minerals
Bat/Medic: 3 scvs on minerals + 1 scv on gas
Vulture: 4 scvs on minerals
Tank: 5 scvs on minerals + 2 scvs on gas (Note that in terran production the unit's production time is the time you have to wait before making the next one, unlike the zerg where all larva spawn equally fast. So, theoretically, 6 scvs on minerals + 3 scvs on gas will get you the same amount, but your tank won't finish in the factory so you can't make the next one right away, that leads to excess money, which means you wasted time on extra scvs, and your army is not as big as it could be.)
Science Vessel: (god I hate this unit...irradiate is so imba) 2 scvs on minerals + 3 scvs on gas.
Goliath: Omitted due to laziness, hey I'm not responsible for you Terrans.
Battle Cruiser/ wraith/ valkyrie: Omitted due to laziness.
I do want to note however, that zerg has the highest mining efficiency due to it's expansion tendencies, and mining efficiency doesn't really affect zerg. But a terran will experience diminishing mining efficiency, so when you do the calculations, make sure you add a few scvs to balance out the efficiency factor. I know pros make about 4-5 more scvs for that purpose.
So if you are the terran who always has 3000 minerals in the bank and you never have big enough of an army, always miss your attack timing due to army size, it is likely that you are making too many scvs. Do the calculations yourself to see if that is the case. If not, you need to practice keeping all your barracks flashing all the time...that's not what this guide is for. Peace
good testing 
