Chicken Math Made Easy

Discussion in 'Coop & Run - Design, Construction, & Maintenance' started by Howard E, Jan 23, 2017.

  1. Howard E

    Howard E Chillin' With My Peeps

    Feb 18, 2016
    With Spring fast approaching, and knowing a lot of folks new to raising chickens are going to be shopping for housing or banging together coops and housing them, I thought it might be helpful to offer a summary of some math factors related to raising laying hens for all these well meaning new growers to follow. Things that may not be obvious to casual observers. Hopefully, it will help eliminate a lot of mistakes born out of inexperience and lack of information.

    How many birds?

    First question new growers often ask is how many birds will so and so coop house? To me, that is backwards. The first question I'd ask is how many eggs do you want if some measure of egg production is the primary motivation for getting birds in the first place.

    Rule of thumb is 3 to 4 birds per dozen eggs per week based on the factor of 3 to 5 eggs per bird per week, which is based upon the knowledge that it takes about 26 to 30 hours for a laying hen to produce a single egg. So birds can't lay an egg every day. There is a plus/minus fudge factor based on breeds, but even so, the very best of them are going to top out at around 280 to 300 eggs per year, with average lifetime production of 500 to 600 eggs per hen. So the high producers (like leghorns and the sex links) burn out after 2 years or so, with the slower layer breeds lasting 3 or 4 years, but with a serious slowdown in latter years.

    But bottom line, take the number of dozen eggs you want per week x 3 or 4 and that is how many birds you want.

    If you want pets and don't care about eggs, that is a different question, but the size factors to follow still apply.

    Housing Requirements:

    So knowing how many birds you want, what then follows is how much building is needed to house them. This is where the wheels fall off. Lash yourself to the mast, the seas we want to navigate are about to get rough.

    Commercial pre-fabs:

    One of the first stops most new growers will make is an Internet search for "chicken coops". Seeking to buy what they need and typically use their personal budget as the basis for price point of what they can afford. These prices will vary from a $100 all the way up to $2,000 or more. The more elaborate (or cute), the higher the cost. The markets are flooded with them. TSC and other farm and home stores all have them as does Craigslist. I am aware of dozens of options for this all built within a few hours of my home.

    Whatever the case, virtually all of them seem to vastly overstate capacity, many suffer from build quality and invariably are disappointing when placed into service. Here is an example of one offered by a local farm and home store. Note the capacity and basis for it:


    I could never understand where they get such ridiculous numbers until I started doing some research on them. What I found is somewhere between fascinating and disturbing beyond belief.

    So for starters, here are a few tried and true historic numbers. Capacity factors that go back at least 100 years.

    Standard Breed (RIR, NH, PR, etc) Layer Capacity: 4 SF per bird

    Smaller Breeds (Leghorns, etc). 3 SF per bird

    Size of Runs: Universal "rule of thumb" for this is 10 SF per bird, although I have yet to find any scientific basis for this anywhere. It is simply something that exists and is treated, and repeated, as a rule of thumb (dogma?) with no more basis in fact than I have offered here. It just is. If you think this is something bizarre, wait until you find out what the standard for "free range" is. It will blow your mind.

    The numbers are for housing in which birds might be expected to be confined in year round, although most were also allowed outside the house most of the time. Houses of this type included all appliances, such as feeders and water pans INSIDE the coop, so birds could be kept in if needed. These were for small sized flocks of 50 birds or less. I have a "modern era" poultry husbandry book, written by a college professor for poultry husbandry classes, from about 50 years ago, just as small farm flocks were being replaced by larger commercial flocks of 500 birds and up, and the standard of 3 to 4 SF per bird was still in force.

    (Before we leave this segment to explore what is to follow, I would like to say here and now, almost ALL growers would be best served to explore ways to either build their own coop or hire someone local to help them. Take whatever number you want to use for capacity in SF per bird, then divide the overall cost of a coop by that capacity and that will give you the UNIT COST PER BIRD. That is your apples to applies comparison. Compare the cost of your prefab to the cost of materials that you can bang together for yourself and most likely you will end up with twice the coop for less cost if you build it yourself. And it will be a better coop to boot. Just saying.)

    So where do these new standards come from? As small flocks were replaced by larger commercial flocks beginning in the 1950's and into the 60's, the pattern of development rapidly went to greater and greater confinement. Growers and researchers just kept pushing the envelop until the end game was reached...... the maximum possible capacity of environmentally controlled housing was achieved. The end result was the battery cage or caged layer house. Birds packed into cages with no more than 3/4 SF per bird……. an area about the size of a single sheet of standard sized copy paper. Ouch.

    Seeing as how that is a rough place for a bird to be, folks concerned about animal welfare got involved to back that off some. Some, but not nearly as much as you might think. If you go shopping for eggs in the store, you will see plain old eggs (which most likely came from birds housed in battery cages; "cage free", "free range" and in some extreme cases, "pasture raised". For the most part, these are standards developed by animal welfare groups and as such, most of us would be shocked to see how much even these capacities differ from those of the past.

    But these standards seem to be the basis for what appears to be the outrageous claims of the small coop makers.

    This is the link to one of the governing sites, so this may be the basis for these numbers:

    What you can also find at this site is a link to a .pdf document that offers a summary of what this group lists as their parameters for the humane production of laying hens.

    I dare say not ANY of us meet these standards or understand why they exist. One also notes there are given numerical factors (such as nests per bird) which are OBJECTIVE, while other factors, such as amount of ventilation are simply listed as "needs adequate amount of", which are highly SUBJECTIVE. So even these folks can't always be relied upon to tell you what is right.

    I encourage every single person reading this piece to go to the site and download or review these parameters.

    There are things there that will be eye openers for most and ruffle the feathers of many. For those of you who are advocates of things like roosts made with 2 x 4's, flat side up, you are not going to be happy.

    Crib notes version from the Humane bunch is as follows:

    Space Requirements

    Cage free: 1.5 SF per bird. Most likely this is where the space requirements used by the pre-fab bunch come from. DO NOT USE this for home built coops. Stick with the traditional number of 3 to 4 SF per bird.

    Free range: 2.0 SF per bird (need access the outdoors) This is essentially a bad joke, since birds do not need to go outside, only have access to the outside. And no mention of how much space needed when they get out there. Or do they? Did I read somewhere if they have access to the outside, the outside needs to be 2 SF per bird and if that is the case, inside can be 1 SF per bird?

    Pasture Raised: Need access to outdoor space equal to no more than 1,000 birds per 2.5 acres, which translates to 108 SF per bird. There are additional requirements regarding what constitutes "pasture" and rotational requirements, etc.

    Pasture per Bird: 50 Birds per Acre (875 SF per bird). Not an official standard, but again, one of those historic rules of thumb. Basically, the amount of birds you can maintain on an area in which the vegetation is likely to survive and can utilize the manure from the birds without leading to a toxic buildup of excessive nutrients such as N-P-K and Ca from the manure. That is roughly 30' x 30' per bird over the long haul. That is a lot of ground!

    Ventilation Space: Standards don't say, except "it needs to be adequate". One book I have doesn't give a set number, only that it needs to be adequate to maintain levels of Ammonia, C02, dust particulates, etc, below levels measured in PPM. I don't have a ruler that allows me to measure that, so that is no help to me at all. Rule of thumb is 1 SF of vent space per 10 SF of floor area.

    Roost Space: Minimum of 6 to 8 inches linear space per bird, with lessor numbers for leghorns and such and more space for larger breeds. Good rule of thumb is 10 inches of space per bird, and I prefer more than one so birds can jostle for position without getting knocked off. BEST size is 1.5" x 1.5", with top surface rounded over. Place at a minimum 10" from back wall and at least 12" apart. All roosts should be on the same level. As per the humane bunch, minimum 18" off the ground and no more than 36" or so maximum, and height must allow for glide path landing space coming off the roost of no more than 45 degree angle. Yes, it is that specific.

    Nest boxes: Allow no less than 1 nest box per 5 birds housed. Size should be a minimum of 12" square, but only if a person is housing leghorns. Larger breeds need larger boxes on the order of 14" or so square. Top of nest box sloped about 30 degrees or more to keep birds form sitting or roosting on top of them. A lot of people use a lot of things, (buckets, etc) so use whatever you like, but those are the rule of thumb standards for nest box size.

    As an aside, some of the more laughable coops seen on BYC have more nest boxes than birds they propose to house. One of the worst examples was a coop they built on episode of "Good Old House". It was truly horrible.

    Water: Adult laying hens will consume an average of about 8 oz (1 cup) of water per day. Are you aware that humane standards suggest this water needs to be kept within a range of between 50F and 80F? I was not. They say it is. So access to clean water at all times is one of the absolutes bird can never be left without. BTW, standards suggest only 1 nipple waterer per 12 birds. I would think 2X to 3X that would be better. Water needs to be kept fresh, so changed often. I prefer buckets with cups and nipples vs. the inverted bell jars so often found in feed stores. I refer to the bell jars as "foul jars" vs. "fowl jars". I have yet to see one that offers clean water for more than a few minutes after it is filled.

    Feed: Laying hens will consume about 3 to 4 oz of layer feed per day. Convert that to pounds x number of hens and that is the amount of feeds you can expect your birds to consume. Standards and most authorities on the subject will tell you it needs to be made available free choice at all times. But if you want to play with the economics of it, take the cost of a sack of feed, divide it by pounds per sack, and that should get you to feed cost per bird per day. Better yet, per week. Then divide by eggs per week and you should get some idea on how much the feed cost is for each egg produced.

    Some other rules of thumb not related to math, but important just the same.

    Avoid uninsulated metal roofs and sides. They result in condensation leading to something looking like it had rained inside. Better to use wood of some type and shingles. Metal is OK if it is insulated, but birds will peck at and eat it, so insulation needs to be covered.

    Speaking of insulation, one book suggests a chickens comb will begin to freeze at +6F. Most likely it was referencing long combed birds like leghorns and roosters, but if you live in USDA climate zone 6a or lower (colder), consider adding insulation to your building. It is not for heat as you think it is. Each bird we have is a little mini furnace radiating several btu's of heat. In a cold climate, a coop can be kept warmer and dryer if the heat generated by the birds is trapped within by insulated walls and ceiling. As much as 10 to 20 degrees warmer depending on a lot of factors, including the number of birds and space they are housed in. Bottom line is if the building is done right, supplemental heat in any form is hardly ever needed, even in climates where outside temps fall to -20 or more.

    Supplemental light:

    Supplemental light is used in nearly all commercial houses to keep birds laying, but seldom is used in backyard flocks, or at least think of it as not being required. Standards, however, suggest at least 6 hours MINIMUM light is needed regardless of location. At the same time, the same standards also suggest at least 6 hours of DARKNESS is also needed, again at a minimum.


    OK, that is a good start on my summary of Chicken Math. I will probably edit this at time goes on and no doubt others will feel compelled to chime in with their own ideas. Keep in mind, however, if I have soiled your shrine with so much chicken droppings, feel free to set me straight, but please do so with some basis in fact beyond your own anecdotal evidence.
  2. Ridgerunner

    Ridgerunner True BYC Addict

    Feb 2, 2009
    Northwest Arkansas
    I’ll admit I only go about halfway through those standards before I gave up. To me a lot of that that looks like standards for large commercial laying flocks with mechanical manure management systems, lagoons that can be flushed or conveyor belts. If I tried to manage my small number of chickens in those tight square feet per chicken spaces I’d be out there managing the manure a lot more than I do now. I just don’t see those as very relevant to our small backyard flocks.

    Nothing scientific to back up my opinion but wow!
    1 person likes this.
  3. Howard E

    Howard E Chillin' With My Peeps

    Feb 18, 2016
    Perhaps I didn't make it clear, but the issue of cramped space per bird was a big part of what I intended to convey. You are correct......these standards are being used by facilities housing hundreds of thousands of birds per site. To give a reader some perspective, Google "Cage Free Layers" and then click on Images. That will offer a visual cue as to the cramped conditions that even so called "humane" organizations say is tolerable. Keep in mind, these birds are housed under very carefully controlled environmental conditions re: feed, water, heat, cooling (?) and ventilation. Manure is removed mechanically on a daily basis.

    Most backyard growers do not go this route, yet the Pre-Fab coops we see advertised DO assume that level of capacity, so in that regard, are misleading to potential buyers.

    Our folks need to stick to the historic numbers as far as SF space per bird. The rest, however, is interesting. There are a whole lot of parameters in there that need to be considered. The poultry pasture standard is a good one for us to use regarding how many birds we can keep in backyards.
    nminusyplusm likes this.
  4. Howard E

    Howard E Chillin' With My Peeps

    Feb 18, 2016
    One of the most misleading standards out there is the "free range" standard. The name alone conjures up visions of birds free to roam about as they see fit and is what most consumers think of when they see that name on the carton. Read the standard. It's not what we think it is.
    nminusyplusm likes this.
  5. Folly's place

    Folly's place True BYC Addict

    Sep 13, 2011
    southern Michigan
    Howard, thanks for taking the time to present this information! New 'chicken fans' don't know about it, and that's why so many get in so much trouble, getting those little prefab coops, and generally not knowing anything about livestock management. I'm too lazy to write volumes; so glad some of you will do that. Mary
    nminusyplusm likes this.
  6. Dmontgomery

    Dmontgomery Chillin' With My Peeps Premium Member

    Apr 1, 2014
    Longville, La

    Yeah, USDA thinks 5 minutes in the open air is free range?! Outrageous!!!
    Yet looking at all these regulations and guidelines makes me wonder how the producers are able to sell chicken at the grocery store at such low prices. No wonder the small farmer couldn't compete.
  7. Howard E

    Howard E Chillin' With My Peeps

    Feb 18, 2016
    How do they do it? Volume. There are only a handful of battery cage companies that produce all those eggs, although with the emergence of the cage free and free range standards, a whole new group of smaller scale growers have come into play. We have a couple kids near us who do raise their birds "free range" and that is true in every sense of the word. They open the gate and let em go. They run free over the farm's building site, as well as adjacent corn fields. But most are NOT like that. The strange thing about the "free range" standard is they only need to have access to the outdoors. Nobody says they have to actually go outside. If you don't put feed and water out there, or even near the door, most won't. The humane bunch's standards recognize this, so make some mandates along those lines, but it is still not what consumers think it is when they see "free range" on the egg carton in the store. The "poultry pastured" flocks are much closer to what we do now and what the practices were years ago when all the small farms raised the birds. But once you do that, you also increase all the management and weather related risks, along with predators, etc. But if you want to compare apples to apples as far as the cost of eggs in the store vs. what you raise, that is the product to compare to.

    But back to those million plus bird facilities. If we buy or build a coop for $500 and it will house 5 birds, our building cost is $100 per bird. A mega facility's cost is somewhere between $5 and $10 per bird and those buildings will last for 20 to 30 years. Their biggest risk is feed cost, although many of them are able to buffer those by using the futures markets to lock in profits a year or so in advance. If you get there in the morning when the packing line is running, it is a sight to behold. A river of eggs about 4 to 5 feet wide riding in on an Anaconda that stretches out about 1/4 mile into the horizon.
  8. Howard E

    Howard E Chillin' With My Peeps

    Feb 18, 2016
    Again, if you folks get a chance, do download and attempt to wade through all those standards. Forget the size factors of cage free and free range and look at the other stuff related to best management practices and how the coops are setup as far as nests, roosts, feed, water, etc. It goes beyond humane treatment towards the comfort, safety and productivity of the birds. A lot of new folks have no experience with any of this, so consider these as guidelines to follow if at all possible.
  9. Howard E

    Howard E Chillin' With My Peeps

    Feb 18, 2016
    I understand and appreciate the time involved. I look at from the other side of the coin. If I can spend the time to do this once, I may not have to do it 5x a day for the rest of my life. [​IMG]
  10. IdyllwildAcres

    IdyllwildAcres Overrun With Chickens

    I think the dirty secret about cage free hens is that they are still cramped for space, never see daylight in many cases and since the cages are gone and they are cramped the start to eat each other:(

    I am a vegetarian mostly born out of the ick factor of factory farming conditions, Oh and the whole "pink slime" issue that came up a few years ago. I am not a vegan, although I lean that way I love eggs and cannot wait to stop buying factory farmed eggs.


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