Three limits, three different days
A brooder has more than one thing that can run out, and the arithmetic for each is the same shape with different numbers in it. Take a capacity you have, divide by the number of birds, and ask on what day the growing per-bird requirement reaches it. The page draws a straight line between the day-one figure and the move-out figure you enter, and solves for the crossing.
On the defaults — 40 birds in 32 square feet, over 42 days — the floor requirement runs from 0.25 square feet a bird to 0.9. Forty birds want 10 square feet on the first morning and 36 on the last. The 32 square feet available is reached on day 35.5.
The feeder is 8 feet, which is 96 inches, and the requirement runs from 1 inch a bird to 3. Forty birds want 40 inches on day one and 120 on day 42, and they hit 96 on day 29.4. The drinker is 3 feet, 36 inches, running from 0.4 to 1 inch a bird: 16 inches on day one, 40 on day 42, crossing 36 on day 35.
The floor is not the one that goes first
Six days before the floor and five and a half before the drinkers, the feeder line runs out. That is the useful part of doing all three, because floor area is the number everybody sizes a brooder on and on these figures it is the last of the three to bind rather than the first.
The reason is in the ratios rather than in anything about birds. The feeder starts at 42 percent used on day one and has to reach 125 percent of what is there; the floor starts at 31 percent and reaches 112.5. The constraint that binds first is the one with the least headroom relative to how fast its requirement grows, and headroom on day one tells you almost nothing about which that is. The drinkers are the fullest of the three on day one at 44 percent, and they still bind five and a half days after the feeder, because they only have to reach 111 percent.
Change any of the six figures and the ranking can invert. That is exactly why the page computes all three and names the first rather than printing a rule about which usually goes first.
Working backwards to a placement number
The other way to read it is the last day. Thirty-two square feet at 0.9 a bird carries 35 birds; 96 inches of feeder at 3 inches a bird carries 32; 36 inches of drinker at 1 inch carries 36. The lowest of the three is 32, and that is the placement number that reaches day 42 on every one of your own figures. Forty were placed, so on these numbers something has to change before day 29 — more feeder line, fewer birds, or an earlier move.
Which of those is the right answer is not a question a page can settle. It depends on what else is available, what the birds are for and what your own guidance says. The arithmetic says the three numbers and stops.
Cycles, not batches
Forty-two days in and ten days out is a 52 day cycle, which is 7.02 cycles in a year and seven whole batches. At 40 a batch that is 280 birds through one brooder; at 32 it is 224. The rest period is a biosecurity decision and it is on the form as a field for that reason, not because there is a number here.
Bedding runs alongside it: 3 inches over 32 square feet is 8 cubic feet to start, plus 4 a week for six weeks, which is 24 more. Thirty-two cubic feet a batch is two bales at 20 cubic feet each, and 12 bales a year across the seven cycles. The volume coming out at the end is more than that, because the birds have added to it and this figure does not count what they added.
A straight line through two points
The ramp is the weakest part of the model and it is worth saying plainly. Birds do not grow linearly, the curve is different by breed and season, and a straight line drawn between a day-one figure and a move-out figure will be wrong in the middle — generally optimistic early and pessimistic late, or the reverse, depending on the species. What the model does well is show that the three limits separate and by roughly how much. What it cannot do is tell you the day to the hour.
Questions people ask
How big does a chick brooder need to be?
That depends on the space per bird you work to, which is a field on this form and not a figure this page holds. What it can do is show you when each limit binds: at the defaults, 40 birds in 32 square feet with the floor requirement running from 0.25 to 0.9 square feet a bird over 42 days reach the floor limit on day 35.5 — but they reach the feeder limit on day 29.4, which is the one that actually goes first.
Which runs out first in a brooder, floor space or feeder space?
Whichever has the least headroom relative to how fast its requirement grows, and that is not the one with the most room on day one. At the defaults the feeder starts at 42 percent used and the floor at 31, and the feeder still binds six days earlier. The page works all three out and names the first rather than asserting a general answer, because changing any of the six per-bird figures can invert the order.
How many chicks can I put in a brooder?
The page reports the number that reaches the last day on each of your three figures and takes the lowest. At the defaults that is 32 — from 96 inches of feeder line at 3 inches a bird — against 35 on the floor and 36 on the drinkers. That is arithmetic on figures you supplied and it is not a recommendation, a welfare judgement or a compliance statement.
How many batches a year can one brooder do?
Days in the brooder plus your cleanout and rest interval gives the cycle. Forty-two days in and ten out is 52 days, which is 7.02 cycles in a year and seven whole batches. The rest interval is a field because it is a biosecurity decision rather than an arithmetic one, and it is not answered here.
Does this cover brooder heat or temperature?
No, and deliberately. There is no temperature, no heat source, no ventilation rate, no light schedule and no health figure anywhere on this page, because those are veterinary and husbandry questions rather than arithmetic. The page works floor and line space against the day the batch grows into them, using figures you provide.