The room is sized by the peak, and the peak has two halves
Stock in a back room follows a sawtooth. It jumps when the delivery lands, falls as the shop pulls from it, and jumps again. The room has to hold the top of that sawtooth, which is the delivery quantity plus whatever buffer was sitting underneath. At the defaults — 620 cases a week, two deliveries, a 150-case buffer — the peak is 460 cases even though the average across the cycle is only 305.
The half that responds to delivery frequency is the cycle half. Go from two deliveries a week to four and the delivery quantity halves from 310 to 155, so the peak falls from 460 to 305 — a third, not a half, because the buffer never moved. Go from four to eight and the peak falls from 305 to 227. The returns shrink every time, and they shrink towards the buffer, which is a floor you cannot get under by ordering more often.
That is the whole reason the first extra delivery a week is worth so much more space than the fourth. If you are trying to get a range into a room that will not take it, adding one delivery is usually the change with the most room in it, and adding a fifth is usually not.
The floor arithmetic is brutally coarse
Positions come in whole pallets, pallets come in whole stacks, and a pallet footprint is about thirteen and a third square feet whether it is full or holding four cases. So the storable floor moves in steps of that size and the peak case count gets rounded up twice on the way to a floor area. Nine pallets two high is five positions, not four and a half.
Run the defaults and the tension is real: 150 square feet of stockroom with 45 percent kept clear leaves about 82 square feet of storable floor, which takes six positions. Two deliveries a week needs six. One delivery a week needs ten, and does not go in. The room is not deciding how much stock you hold; it is deciding how often the truck has to come.
What the clear share is really for
Forty-five percent of a small stockroom sounds enormous until you stand in one. You need the route from the back door to the shop floor, the space in front of every shelf, somewhere for the cage to sit while it is being emptied, and access to whatever panels and equipment live back there. The number is an input on this page rather than something calculated, and that is deliberate: what has to be kept clear in front of an exit, an electrical panel or a sprinkler head comes from the code your jurisdiction has adopted and from your fire official, and it is not something a calculator gets to assert.
The failure worth naming is the ordinary one. A back room fills up over a busy fortnight, the overflow goes in the walkway because there is nowhere else, and the route to the back door stops being a route. That is not a tidiness problem. It is the reason the clear share exists as a number at all, and it is the first thing to check when the calculator says the peak does not fit — because it will fit somewhere, and the somewhere is usually the walkway.
The two costs and the one this page cannot see
Deliveries cost money and floor costs rent, and those pull in opposite directions: more deliveries, less floor. With the optional cost fields filled in, the table prices both across one to seven deliveries a week and marks the cheapest option that actually fits the room. At the defaults the arithmetic prefers fewer deliveries, and the room refuses it — which is a fair summary of how the decision usually goes in a small shop.
What is missing is the cash. Holding 460 cases instead of 305 is money sitting in a back room, and it is not priced here. Neither is the risk side: ordering more often means more occasions on which a delivery can arrive short or late, and fewer means each shortage hurts for longer. If the cash matters to the decision, inventory turnover puts a carrying cost on it and the inventory order calculator handles reorder points and order quantity properly.
Related pages
The stockroom percentage you assumed when planning the shop is set in the store fixture run layout calculator, and this page is the test of whether that assumption survived. What comes out of the room and onto the deck is the shelf facings and days of cover calculator. For a back room that is really a small warehouse, the pallet rack layout calculator and the warehouse cube utilization calculator take the same geometry further, and the pallet load planner works out cases per layer and layers to a height limit.
Questions people ask
How big should a shop stockroom be?
The question only has an answer once you fix the delivery frequency, because the room holds the delivery plus the buffer, not the weekly volume. Work out cases per delivery, add whatever you never let the buffer fall below, convert to pallets and then to floor positions, and add the share of the room that has to stay walkable. Doing it the other way round — picking a percentage of the shop and hoping — is how back rooms end up with stock in the walkway on a Monday morning.
Do more frequent deliveries really save space?
They shrink the cycle half of the peak and leave the buffer untouched, so the saving is real but it tails off fast. Halving the delivery quantity does not halve the peak. At the defaults here, going from one delivery a week to two removes about 40 percent of the peak; going from four to five removes about a tenth of it. If space is the problem, the first extra delivery is where nearly all the benefit is, and it is usually the only one worth negotiating for.
How many cases fit in a stockroom?
Storable floor divided by the pallet footprint gives whole positions, positions times how high you stack gives pallets, pallets times cases per pallet gives cases. The rounding is severe — a pallet footprint is claimed whether the pallet is full or nearly empty — so a room that looks like it should hold nine positions often holds six. Stack height should be whatever you can safely place and retrieve with the equipment you actually have, which for most small shops is hand height, not what the shelving is rated for.
What percentage of the stockroom has to stay clear?
This page takes it as your input and states no figure, because the answer is not a retail rule of thumb — it comes from the code your jurisdiction has adopted and from your fire official, and it depends on where your exits, panels and sprinkler heads are. What is worth saying is that people consistently guess low. Once you have accounted for the route to the back door, standing room in front of every shelf, and somewhere to work a delivery, the clear share in a small room is usually a lot more than a third.
Should I hold less buffer stock to save room?
It is the one lever that moves the trough as well as the peak, so it frees space at every point in the cycle rather than just at the top. It is also the lever that decides what happens when a delivery is short or late, so cutting it is a decision about risk rather than about storage. The useful framing is to price both sides: this page shows what the buffer costs in floor, and inventory turnover shows what it costs in cash, and the answer to how much you need is a supplier reliability question that neither page can answer for you.