Boxes on a route is gaps plus one
A 1,200 ft route at 300 ft spacing has four gaps, and four gaps have five endpoints. Five boxes, not four. This is the same fencepost count that catches people laying out anything along a line, and getting it wrong here costs a whole post, a whole guard and a whole box.
The end to end span is then 1,200 ft, which is 0.23 miles, and one check round on foot is twice that. That last figure is worth having before the run is laid out rather than after: at five boxes it is half a mile, at twenty boxes on the same spacing it is two and a quarter miles each way. A run is a commitment to walking it.
Post length adds up faster than it looks
The post is embedment, plus the height to the box floor, plus the box, plus whatever sticks out of the top. Two feet in the ground, six feet to the floor, a one foot box and three inches above is 9 ft 3 in of post for a box whose floor is six feet up. People buy eight foot posts for a six foot mount and are a foot and a quarter short.
| Height to box floor | Post length needed | Posts from a 10 ft stick | Posts from a 12 ft stick | Posts from a 16 ft stick |
|---|---|---|---|---|
| 4 ft | 7 ft 3 in | 1 | 1 | 2 |
| 5 ft | 8 ft 3 in | 1 | 1 | 1 |
| 6 ft | 9 ft 3 in | 1 | 1 | 1 |
| 8 ft | 11 ft 3 in | 0 | 1 | 1 |
The 4 ft row is the only one in that table where a longer stick buys anything: a 16 ft stick carries two 7 ft 3 in posts with very nearly 1 ft 6 in over. Every other row is one post per stick regardless, and the whole difference between the sticks is how much you throw away. That is the argument for choosing stock length against the post length rather than buying whatever is on the rack.
The zero in the 8 ft row is real too. An 11 ft 3 in post does not come out of a 10 ft stick at all, and the calculator says so rather than quietly rounding.
The offcut is the whole cost of getting the stock length wrong
Five posts of 9 ft 3 in out of 10 ft sticks is five sticks and 9 inches wasted on each — 3 ft 9 in over the run, 7.5 percent of the stock. The same five posts out of 12 ft sticks is still five sticks and 2 ft 9 in wasted each, which is 13 ft 9 in and 22.9 percent. Buying longer never helps unless the extra length crosses the threshold for a second post.
A wrap is a rectangle, and its width is a circumference
Sheet wrapped around a post takes a piece as wide as the circumference plus the overlap where the two edges meet. A 3.5 in post has a circumference just under 11 in, and with a 2 in overlap the piece is a shade under 13 in wide by whatever height you want. At 24 in tall that is 311.9 square inches, 2.166 square feet a post, 10.83 square feet for five, and 11.91 with ten percent waste.
Two notes on that. A square post measured across the flats under-reads slightly, because a wrap round a square section follows four flats and four corners rather than a circle, and the calculator uses the circle. And the overlap is not optional: a wrap with no overlap has a seam with nothing to fasten to.
What the page does not do, on purpose
It does not say how far apart to put boxes, how high to mount them, which way they should face or how far from anything they should be. Those are species and site questions and the sources for them are your state wildlife agency, your county extension service and the published plans conservation organisations put out. The spacing and height fields exist so the arithmetic has inputs, not because the defaults mean anything.
It also does not touch how the post is set. Tamped, gravelled or concreted is a soil, frost depth and wind question and it is genuinely local. And it makes no judgement about whether any of this will be used, because a take-off cannot know that.
The thing this page will say plainly: mounting work at height is where this project hurts people. A box, a bracket and a drill at the top of a ladder in a field is a two person job with the ladder footed, and the arithmetic above does nothing to change that.
Where this hands off
For hole size, concrete or gravel per hole and the rest of a fence line, the fence post calculator does posts, rails and bags. Building the boxes that go on these posts is the nest box cut list calculator, a panel structure is the bat house chamber calculator, and a drilled block is the nesting block drilling calculator. If the structure is going on a wall rather than a post, wall mount fastener load covers the fixing side.
Questions people ask
How far apart should the boxes be?
This page has no figure for that and will not offer one. Spacing depends on the species, the habitat and the region, and it is exactly the sort of number that should come from your state wildlife agency, your cooperative extension office or the published plan you are working from. The spacing field is here so the count arithmetic has an input. What the page does tell you honestly is the consequence of whatever you enter: the box count, the span, and how far you will be walking to check them.
Why is my post so much longer than the mounting height?
Because the post is the embedment plus the mounting height plus the box plus whatever runs above it. Two feet in the ground and a six foot mount with a one foot box and three inches proud is 9 ft 3 in. The mounting height is only about two thirds of the post. This is the single most common reason a load of posts turns out to be short.
Is it worth buying longer post stock?
Only when the extra length crosses the threshold for a second post out of one stick, and usually it does not. At 9 ft 3 in a post, a 10 ft stick gives one and a 16 ft stick also gives one, so the 16 footer just wastes 6 ft 9 in instead of 9 in. At 7 ft 3 in a post a 16 ft stick does give two. Work out your own post length first and then pick the stock, rather than the other way round.
Does the calculator include the concrete for the holes?
No, deliberately. How a post is set — tamped backfill, gravel or concrete — depends on your soil, your frost depth and your exposure, and none of those are things this page knows. The fence post calculator does hole volume, gravel and bags of mix on a given hole size, and that is the right place for it. This page stops at how much post you are buying and how much of it you are throwing away.
Can I take a box down or move it once it is up?
Ask your state wildlife agency before you do. Most native birds are protected, an occupied nest carries its own protections that are separate from the structure, and both what is allowed and when it is allowed differ by state and by season. That applies to cleaning and repairs as much as to removal. This page produces a material list and nothing on it is a statement about what you may do to a box that is already in use.