12×12×12 nest box, 1 per 4 hens, mounted below the roost

The single rule that decides whether a nest box gets used or fouled: mount the top of the box lower than the top of the roost. Chickens sleep on the highest perch in the coop. Build a box level with — or above — the roost and the flock sleeps in it, drops in it, and the eggs come out covered in the next morning's litter. Build to 12×12×12 inches for standard breeds (14×14×14 for heavy breeds, 10×10×10 for bantams), one box per 4 hens, mounted at least 18 inches off the floor but always under the roost.

The 1-per-4-hens ratio and 12×12×12 dimensions are the published Cooperative Extension figures; the height stack-up and the internal-vs-external decision are HatchMath methodology — practitioner consensus across extension small-flock guides, not a single sourced number. The most-skipped detail in most write-ups: hens share. A 12-bird flock with five boxes will use 1–2 favorites and ignore the rest. The extras earn their lumber at peak-laying windows and when the dominant hen camps in the favorite — not in raw count terms.

Standard backyard nest box: 12×12×12 in, 18+ in off floor, sloped roof, front lip retains bedding.

Box count: 1 per 4 hens, never fewer than 2

Flock size	Boxes	Note
1–4 hens	2 boxes (working minimum)	Even with 1–2 hens, build at least 2 in case one is broody
5–8 hens	2 boxes	Hens share favorites; spare doesn't go unused
9–12 hens	3 boxes	Peak-laying hours need a second option
13–16 hens	4 boxes	Standard 1-per-4 ratio
17–20 hens	5 boxes
21–24 hens	6 boxes	Beyond ~20 birds, run two box clusters at opposite walls

Build to 1-per-4 and don't overthink it. I'd round up before I'd round down — an extra 12×12 box costs maybe $8 in plywood and a half hour with a circular saw, and it pays back the first time a subordinate hen needs an option that isn't the favorite. The 1-per-3 nudge is worth it for flocks with a history of egg-eating (extra choices mean an egg is less likely to sit unattended in a crowded box where it can get pecked and broken). The 1-per-5 cold-climate compression you'll read about elsewhere is real but marginal — I wouldn't plan around it.

Build 12×12×12 unless you have heavy breeds

Breed class	Box size (W×D×H)	Notes
Standard breeds	12×12×12 in	Leghorn, RIR, Plymouth Rock, Sex-Links, Australorp, Wyandotte
Heavy breeds	14×14×14 in	Brahma, Cochin, Jersey Giant, Orpington (large lines)
Bantams	10×10×10 in	Silkie bantam, Cochin bantam, Sebright
Mixed flock	12×12×12 in	Build to the smaller of the breed range; bantams won't mind extra space

Bigger than spec is fine; smaller is not. A box too tight makes a hen stand awkwardly while laying, and she'll go find a better spot — the corner of the run, the woodpile, behind the coop. For a mixed flock with a couple of bantams alongside standards, build to the standard 12×12×12; the bantams won't mind extra space and you don't want a Brahma wedged into a 10×10. Sticking with 12×12×12 covers 90% of backyard flocks.

Mount the box below the roost — the rule that fouls eggs when broken

Three numbers run the height stack-up:

Minimum 18 inches off the coop floor. Below 18 in, mice and rats reach eggs more easily, and run-and-jump predators (a determined raccoon, a fox under a coop) have a clearer path. Free-standing boxes built at coop-floor level also collect dust and bedding kicked up by chickens scratching.
Below the top of the roost. Always. The roost is the highest perch in the coop; hens roost on the highest available spot. If the box top is at or above roost height, hens sleep in the box overnight. You wake up to droppings in the laying litter and fouled eggs.
Reachable for collection.External boxes that protrude through the wall let you collect from outside. Internal boxes need a clear path inside the coop. If you have to crawl over the roost to reach the boxes, you'll skip collection during bad weather and eggs will pile up.

Stack-up for a 6-ft-tall coop, floor to ceiling: bedding sits at 4 in; the nest-box bottom at 18 in off the floor (so the box top lands near 30 in for a 12-tall box); the roost runs 40–48 in, clearly above the box top. That gap is what keeps roosting where roosting belongs and laying where laying belongs. If your coop forces the boxes higher than 18 in, raise the roost to match — never let them cross.

Internal under 8 birds, external past it

The two mounting schemes:

Internal nest boxes live inside the coop, usually mounted along one wall. Cheaper, simpler, warmer. Drawbacks: you walk into the coop to collect, and roost placement matters more (a poorly placed roost above an internal box drops droppings into the box).
External nest boxesprotrude from the coop wall like a small extension, accessed from outside via a hinged lid. Easier collection (especially in winter — no stooping, no wading through litter), simpler to clean, and keeps the laying area cleaner because hens don't track droppings in. Drawbacks: more lumber, a small heat-loss surface in cold climates, and the lid must seal well to keep out drafts and predators.

For my money, the cleaning-time math wins past 8 birds — climate-dependent, but it's the rule I'd build to. Decision matrix:

Situation	Choice
Small coop (4×4 to 4×6)	Internal — saves square footage that's already tight
Standard coop (4×8 to 6×8)	Either; external for ≥ 8 birds
Large coop (8×10+)	External strongly preferred for collection ergonomics
Cold climate (sub-zero winters)	Internal — preserves coop heat envelope
Hot climate (Phoenix, Gulf Coast)	External — extra airflow + cooler eggs at collection

Build details that decide whether the box gets used

Sloped roof, not flat. A 30–45° slope on the box top stops hens from roosting on top of the boxes. Flat-topped boxes create a second sleeping-perch problem on top of the one you just avoided inside the box. Worth the extra cut every time.
Front lip 4–6 inches tall. Keeps bedding and eggs in; gives a hen a sill to step over without it being hard to enter. Too low (under 3 in) and bedding kicks out; too high (8+ in) and pullets struggle to enter.
Privacy curtain (optional).A strip of burlap or fabric across the front, slit so hens can push through. Reduces light inside the box and is associated with reduced egg-eating in flocks where that's a problem. Not strictly necessary.
Hinged lid for external boxes. Use a real piano hinge or two strap hinges; rigid plywood top with water-shedding overhang. A latch or pin keeps it closed against raccoons, which can lift unsecured lids.
Drainage if the box can get wet. External boxes in rainy climates need either a gutter above or small drain notches in the floor. Wet bedding = mold = vacated box.

Drop a ceramic egg in every new box

Pullets entering point of lay don't know where to lay. Without an example, they pick: corner of the run, the floor under the roost, a hidden spot outdoors. The cure is a $2 fix — a wooden or ceramic dummy egg dropped in each box at build time and left there.

Hens are visual; they associate “egg in this spot” with “lay your egg in this spot.” A dollar-store ceramic egg in each box fixes the first-egg problem in most flocks inside 2–3 days. Bonus: porcelain or wooden eggs also help with egg-eaters — the frustration of pecking a non-cracking egg breaks the habit. I'd drop one in every box on day one and forget about them.

Common questions

How many nest boxes do I need for my flock?

One nest box per 4 hens is the published Cooperative Extension figure, with a working minimum of 2 boxes regardless of flock size. A 6-hen flock = 2 boxes; a 12-hen flock = 3 boxes; a 20-hen flock = 5 boxes. Hens often share — even with five boxes available, a flock of 20 will use 1–2 favorite boxes and ignore the rest. The extras matter mostly for peak laying hours when multiple hens want to lay simultaneously, and for giving subordinate hens a private option when the dominant one is camped in the favorite.

What size should a chicken nest box be?

12×12×12 inches for standard breeds (Plymouth Rock, Rhode Island Red, Sex-Links, Australorp, Wyandotte, Leghorn, etc.). 14×14×14 inches for heavy breeds (Brahma, Cochin, Jersey Giant). Bantams are fine in 10×10×10. The box is bigger than strictly needed — extra space lets a hen turn around and settle without compacting the litter into one corner.

How high should nest boxes be off the floor?

18 inches off the coop floor as a working minimum. Critical detail: the top of the nest box must be lower than the top of the roost, otherwise hens roost in the boxes overnight and you get fouled eggs. If your coop dictates higher boxes, raise the roost higher to maintain the order. Free-standing boxes can sit lower (8–12 in) if they don't conflict with roost height.

Internal or external nest boxes — which is better?

External (boxes that protrude from the coop wall, accessed from outside via a hinged lid) are easier to clean and collect from but cost more lumber and create a small heat-loss/draft surface. Internal (boxes inside the coop) are simpler and warmer but require entering the coop to collect eggs and can let droppings reach the boxes if the roost is poorly placed. For a 4-bird flock or a small coop, internal works fine. For 8+ birds, external pays back the lumber cost in cleaning time saved.

What's the best bedding for nest boxes?

Pine shavings (kiln-dried, large flake), straw, or hemp bedding. Pine is the default — cheap, absorbent, easy to refresh. Straw is acceptable but mats faster and holds moisture longer. Hemp bedding is premium but lasts 2–3× longer than pine. Avoid cedar shavings (toxic respiratory fumes for poultry) and dusty fines. Refresh weekly — top up the box, replace it entirely if soiled. A 1–2 in layer of bedding is enough; deeper just gets kicked out.

Why are my hens not using the nest boxes?

Five common reasons: (1) the boxes are higher than the roost — chickens sleep on the highest perch, so they roost (and lay) in the box. (2) The boxes are too bright — direct light makes hens want privacy, so they go find a dark spot somewhere else. (3) The boxes are too crowded or there are too few. (4) New flock with no example — drop a wooden or ceramic 'dummy egg' in each box to mark them as the right place. (5) Recent stress event (predator scare, new flock member) breaks the routine for several days.

By Jimmy L Wu. Reviewed 2026-05-02. The 1-box-per-4-hens ratio and the 12×12×12-in standard-breed dimensions anchor on Cooperative Extension small-flock publications and Damerow's Storey's Guide to Raising Chickens; the 18-in off-floor minimum and the box-below-the-roost rule are extension-published practitioner consensus. Heavy-breed and bantam adjustments, the height stack-up, and the internal-vs-external decision matrix are HatchMath methodology — synthesized practitioner consensus, not numbers extension publications directly state. Not veterinary advice.