The yard is mostly alley
Run the defaults — a 160 by 90 ft yard, 12 ft packs 48 in wide, 12 ft alleys, 24 in between packs along a row — and you get 11 packs down a row and 6 rows, so 66 on the ground and 198 stacked three high. That is 138,600 board feet at 700 board feet a pack. It is also 3,168 square feet of ground under lumber out of 14,400, which is 22 percent. Four fifths of the yard exists so that a machine can reach the packs.
That ratio is not waste and it does not improve much with a bigger yard, because it is set by the width of a pack against the width of an alley. A 4 ft pack in a 16 ft band uses a quarter of the depth it occupies, and stacking three high is what rescues the number — it triples the board feet without touching the footprint at all.
Capacity is a rate times a wait
Sawing 9,000 board feet a month and holding each pack 9 months means 81,000 board feet standing on the yard on any ordinary day. Not 9,000. The default yard holds 138,600, which covers it with room for about 6 more months of dwell, or enough slack to push production to about 15,400 board feet a month at the same 9 months on the sticks.
Get this wrong and the failure is delayed and confusing. A new yard looks enormous for the first few months because nothing has come off it yet. The overflow arrives at exactly the moment the first packs become sellable, which is the moment everybody is least inclined to believe the yard is the problem.
Alleys move in steps
Widening the alley from 12 ft to 14 ft in the defaults drops the yard from 6 rows to 5 — a loss of 33 packs and 23,100 board feet for two feet of width. Narrowing it from 12 to 10 gains a row rather than nothing — 14 ft bands go into 90 ft seven times, so 7 rows and another 33 packs. Alley width buys and costs whole rows, never fractions, so the useful question is never "how wide should the alley be" but "which side of the next boundary am I on".
What this does not decide
Ground bearing, drainage, prevailing wind, how a pile is founded and bound, and whether any of it dries at the rate you are hoping for. This is a packing and inventory problem only. The dwell time you type in is your figure from your own records, and the calculator has no view on whether it is long enough.
Questions people ask
Why does the alley get subtracted once per row rather than once per pair of rows?
Because the arithmetic charges each row a band consisting of its own width plus one alley, and then adds the last alley back at the end. That models a yard where every row has access down one side, which is how single-access rows work. If your rows are genuinely back to back and share one alley between two, enter a pack width of two packs plus the gap between them and treat the pair as one row.
Does the stacking height affect anything except the count?
In this arithmetic, no — packs stacked three high triple the board feet and leave the footprint alone. In your yard it affects a great deal: what lifts them, how the load transfers down through the lower packs, wind exposure and how you reach the middle one when only it is ready. The calculator reports the total pile height including the foundation so you can check it against the machine, and stops there.
Should the dwell time include the kiln?
Only if the kiln is on this yard. Dwell here means the time a pack occupies yard space, so if packs go straight from the yard into a chamber elsewhere, dwell ends when they leave. If they come back out and sit again before shipping, that second period is yard space too and belongs in the figure.
The board feet per acre figure looks low. Is it right?
It is right for the layout entered, and it is low because most of an acre of drying yard is alley. Raising it means stacking higher, using longer packs so fewer gaps interrupt a row, or narrowing the alley — and the last one only helps when it crosses a band boundary. The figure is there mainly for comparing two layouts on the same ground, not as a benchmark against anyone else.
Can I use it for a covered shed rather than an open yard?
The layout arithmetic is the same; enter the usable interior dimensions. The one thing to watch is the stacking height, since a shed has a ceiling and the total pile height output includes the foundation under the bottom pack. Check that figure against the clear height rather than against the eave.