Pounds size the store, baskets size the machines
Two numbers do different jobs here and they get muddled constantly. Total poundage tells you how much washing capacity has to exist. The distribution of basket sizes tells you how to cut that capacity up. A store can have exactly the right total and still be unusable, because everything that is free is a 60 lb pocket and everybody in the room has a 14 lb basket.
The page assumes a customer takes the smallest pocket their basket fits into, which is what they do wherever the vend price rises with the pocket. That single assumption is what turns a capacity sum into a matching problem, and it is also the assumption most worth arguing with — see the last section.
Rounding up three times
Each pocket size is rounded up to a whole machine on its own. That is correct, and it is also why the turns come out uneven across the rows: one group might land at 2.9 machines of work and get three, another at 1.1 and also get a whole machine. The 1.1 row is where the money is. You are buying a complete machine, its plumbing, its drain and its floor for a tenth of a machine of work, and the honest options are to drop that size entirely and push those baskets up a pocket, or to accept it as the size that keeps a particular kind of customer coming in.
That spare capacity is not waste in the abstract. Demand is not smooth: Saturday morning is not Tuesday at two, and the rounding is most of what stops a peak becoming a queue at the door. The calculator does not model the peak, so treat the rounding as the only cushion you have unless you have added one deliberately.
Water follows the drum, not the linen
This is the part that surprises people who came from thinking about laundry at home. A machine fills to a level set by its own drum, so a 20 lb pocket uses very nearly its full water whether there are 20 lb in it or 8. Cost per pound washed therefore moves inversely with fill, and the small pockets are cheaper per cycle but not necessarily cheaper per pound.
The block near the bottom prices this by comparing the water at the fills your basket mix actually produces against a store where every drum ran completely full. No store ever hits that, so read it as a ceiling on what better matching could recover rather than as money currently being lost. The number moves fast with the water and sewer rate, which is why that field asks for the all-in figure off your own bill rather than a rate you looked up.
Where this is wrong
Three places, in order of how much they matter. First, the smallest-pocket-that-fits rule breaks down as soon as the store is busy — people take whatever is free, which loads the big machines more than this says and makes the water figure look worse than the page shows. Second, basket weights are guesses unless you have actually weighed some, and the whole mix pivots on the mean; being wrong by 20 percent on the mean moves every machine count. Third, the running share is doing an enormous amount of work in one field, and it silently contains the dead hours, the abandoned loads and the wait for somebody to come back and unload.
The fix for all three is the same and it is not more arithmetic. Read the machine counters for a fortnight, weigh thirty baskets on a parcel scale, and put your own numbers in. After that it stops being a generic model and becomes a description of your store.
Questions people ask
How many washers does a laundromat need?
It follows from the poundage and the turns, not from the square footage. At the figures in the form — 2,400 lb a day, a 30 minute door-to-door cycle, 16 hours open and machines running 55 percent of that time — a machine gets 17.6 turns a day, and the baskets split across the three pocket sizes into the counts the page prints. Change the running share to 40 percent and the count rises sharply, which is why that field matters more than any of the capacity fields.
What size washers should a laundromat have?
Whatever matches the baskets that come through the door, which is a local question. Enter the spread of load sizes you actually see and the page splits the machines to suit it. A store next to student housing and a store on a road out to farms have the same poundage arithmetic and completely different mixes, and copying somebody else equipment list is how stores end up with a wall of large pockets that turn twice a day.
Does a half-full washer use less water?
Barely. The machine fills to a level set by its own drum, so the gallons follow the pocket and not what is inside it. That is the whole reason the page prices water per pound washed rather than per cycle: the same linen costs noticeably more to wash in a pocket two sizes too big, and it is a cost that never appears on a per-cycle view of the business.
Why does the calculator round each pocket size up separately?
Because you cannot buy nine tenths of a washer. Rounding each group on its own is the honest arithmetic, and the side effect is that the store carries spare capacity in three places at once. That spare is most of your peak cushion. The row worth questioning is any one that rounds up from a very low number, because there you are buying a whole machine and its plumbing for a fraction of a machine of work.
Where do I get the gallons per cycle figure?
From the specification sheet for the machine and the cycle you actually vend, divided by the rated pocket to get the per-pound-of-capacity figure the field asks for. If you would rather measure it, read the water meter across a counted number of cycles on a quiet morning when nothing else in the building is drawing. Both beat any number quoted for machines in general.