One number decides everything
How much covered ground a container block needs comes down to the square inches one container occupies, and that is set by two choices: the centre-to-centre spacing, and whether the rows are offset or squared up.
Square grid, area per container is the spacing squared. Offset rows, it is the spacing squared times 0.866, because each container gets a hexagon rather than a square. The 0.866 is the square root of three over two, and it is the same factor that makes a stack of pipes settle into triangles. It is 13.4 percent less ground for identical spacing between neighbours, which is free floor for nothing but the loss of straight lines in the cross direction.
On the numbers this form opens with, 11 inch containers jammed rim to rim on offset rows take 104.8 square inches each, or 1.37 per square foot. Seven thousand of them is 5,094 square feet of ground, and at 85 percent of the floor usable that is 5,993 square feet of covered house. Set them at 14 inch centres instead and each takes 169.7 square inches, the block becomes 8,251 square feet, and the covered floor becomes 9,707 square feet.
| Arrangement | Sq in each | Per sq ft | Covered floor for 7,000 |
|---|---|---|---|
| Jammed, offset | 104.8 | 1.37 | 5,993 sq ft |
| Jammed, square | 121 | 1.19 | 6,920 sq ft |
| 14 in centres, offset | 169.7 | 0.85 | 9,707 sq ft |
| 14 in centres, square | 196 | 0.73 | 11,209 sq ft |
The spread from top to bottom is 87 percent. Same containers, same count, same houses.
Where the rounding bites
Nobody buys a fraction of a house. At 30 by 96 feet a house is 2,880 square feet, so the jammed offset case needs 2.08 houses and you build three. The 14 inch square case needs 3.89 and you build four. Between those two arrangements the difference is one house for a whole winter — its cover, its heat if it has any, and the labour of filling and emptying it.
The rounding also means the last house is usually well short of full. Three houses is 8,640 square feet against 5,993 needed, leaving 2,647 square feet, which at the jammed offset density is room for another 3,092 containers. That is worth knowing before you decide whether a fourth block of stock can come inside.
The usable share is not a detail
The share of a covered floor you can actually stand containers on is the input people leave at 100 and then wonder why the house filled short. It covers the walkway you need to get down the middle, the strip along each sidewall where a hoop house roof is too low to reach into, the door end, and wherever a hoop foot or a post lands. Eighty-five percent is the placeholder in this form and nothing more than that.
Get your own figure by measuring a house you have already filled: count what went in, multiply by the square inches per container from the spacing you used, and divide by the floor area. That is your real usable share, and it will be specific to your structure and your handling.
What this page will not tell you
It will not tell you whether to jam containers pot to pot, and it will not tell you anything about overwintering at all. Whether a crop needs protection, what temperature anything is held at, what cover goes over it, when it goes in and when it comes out, and what happens to airflow in a jammed block are horticultural questions with answers that differ by species, by region and by year. Your own records and your cooperative extension service are the sources. This page states none of it and issues no verdict about whether an arrangement will work.
What it does is put a number on the space each choice costs, so the decision gets made with the trade-off visible. For the structure that covers the block, hoop house sizing turns a span and a length into a floor area and a covering area, and greenhouse heat loss prices heating it. For the crop that arrives at this point, the potting-up stage calculator gives the count and the container size, and cost per plant turns the square feet into money.
Questions people ask
How much space does a container actually need over winter?
This page has no answer and will not invent one. Spacing over winter is a question about the crop, the cover, airflow, how the block is handled in spring, and in some cases about what fits through a door. It differs by species and by region. The calculator takes whatever spacing you enter, from your own practice or from your cooperative extension service, and tells you the floor it costs. Nothing here is a recommendation about protection, temperature or timing.
Why is jammed spacing set to the container width rather than something smaller?
Because the rims touch at exactly one container width between centres, and they cannot get closer than that without overlapping. If your containers are tapered enough that the bases nest while the rims touch, the width across the rim is still the right figure, since the rim is what stops them. If they are square containers, enter the side dimension and use the square grid pattern, which then tiles exactly with no gaps at all.
Does the offset saving apply to square containers too?
No. The 0.866 factor comes from packing circles, where offsetting the rows lets each row drop into the hollows of the last one. Square containers on a square grid already tile perfectly with zero waste, and offsetting them just leaves triangular gaps. For square pots, use the square grid option and the area per container is simply the side dimension squared with no factor at all.
What if my house is not a rectangle, or the containers cannot go right to the wall?
That is what the usable share field handles, and it is why the house count comes from an area rather than from a packing. A hoop house has a roof that drops to the ground at each side, so the outer few feet are unusable for anything tall, and the usable share on a 14 foot wide tunnel is very different from one on a 30 foot one. Measure your own by counting what actually fits in a house you have filled.
How do I count containers of two different sizes going into the same house?
Run the page twice, once for each container size, and add the two covered floor figures together before dividing by the house area. Do not average the diameters — the area goes with the square of the spacing, so an average diameter understates the space two mixed sizes need. Adding the areas is exact; averaging the sizes is not.