Station count follows from patient numbers, session length and how many shifts the unit will genuinely staff. The arithmetic, the figures you have to source locally, and the two reserves people forget.
Dialysis units in Bangladesh are usually sized by the space available and the budget, and the capacity is discovered afterwards. Working the other way round takes an afternoon and produces a unit that is neither half empty nor turning patients away in its first year.
Maintenance haemodialysis is normally three sessions per patient per week, and a session is normally four hours of treatment plus turnaround. Turnaround is the part that gets left out: the patient off, the machine disinfected, the station cleaned, the next patient on and needled. Plan it from your own unit's observed practice rather than from an ideal.
From there:
That produces the treatment stations. It is not the number of machines to buy, and it is not the number of stations to build for.
The patient number is the input that decides everything, and nobody can give it to you from a textbook. Build it from what your own catchment tells you.
Where the private sector already serves part of the catchment, find out how much and at what price, because affordability rather than capacity may be what determines how many patients actually present to you.
Isolation stations. Hepatitis B positive patients require dedicated machines and a separated area, and those stations cannot be counted in the general pool even when they are empty. Hepatitis C positive patients require dedicated machines under most unit policies. Size these from your own screening data and add them on top of the calculated station count, never inside it.
Machine reserve. Stations are plumbed positions; machines break. A unit running every machine every session has no room for a fault and will cancel sessions. Buy more machines than stations, and keep one commissioned and idle rather than in a box.
The expensive parts of a dialysis unit to expand later are the water treatment plant, the distribution loop, the drainage and the electrical supply. Adding stations to a loop that was built for the current count means shutting the unit down to do pipework, and it is how dead legs get created. Design the plant room, the loop and the drain for the station count you expect in ten years, then install chairs and machines in phases as demand and staffing allow. The water plant behind all of this has its own article on this site.
One constraint overrides the arithmetic. Nursing and technician staffing sets real capacity, not chairs. A unit with twelve stations and enough trained staff for eight runs eight, and the four idle stations are capital sitting still. Confirm the staffing plan before confirming the station count, and if the staffing is not there yet, phase the stations to match it.