Two divisions and everything else follows
Bays come from the run divided by the bay length, rounded up. Lifts come from the working height divided by the lift height, rounded up. After that it is bookkeeping: a run of bays needs one more frame than it has bays at each level, two cross braces per bay per lift, a base plate under every leg of the bottom frames, and a pair of coupling pins at every frame joint going up.
Work the defaults through. Forty-eight feet of wall at seven foot bays is 6.857 bays, so seven bays, and six of them are full — the seventh is six feet. Twenty-four feet of working height at five foot lifts is 4.8, so five lifts, and the top platform lands at twenty-five feet rather than twenty-four. Seven bays and five lifts gives eight frames per lift and forty frames in total, seventy braces, sixteen base plates.
Planking is the count that surprises people. A five foot frame is sixty inches across and a nominal 2x10 scaffold plank is about 9.5 inches wide, so 6.32 planks fit — call it seven, which covers 66.5 inches and overruns the frame by six and a half. Seven planks per bay across seven bays is forty-nine planks for one decked level, and that is the number to order rather than the forty-four you get from dividing areas.
The last bay is never a full bay
Runs are measured in feet and frames come in fixed lengths, so the two almost never divide evenly. That last part bay is where orders go wrong in both directions. Order by area and you are short of planks, because the short bay still needs a full deck — a six foot gap does not take six-sevenths of a plank. Order by full bays and you have paid for length you cannot use, because the frames still tile at seven feet whether or not the wall does.
The practical decision is whether the run stops short of the corner or projects past it, and it is worth making that decision on the ground before the truck arrives rather than at seven in the morning with a crew standing around. If the wall length is anywhere near a bay multiple, moving the start point by a foot is usually cheaper than adding a bay.
What the top platform actually is
Working height is where the work is, not where the platform is. Divide it by the lift height and round up and you get a platform somewhere above your working height rather than at it, which is normally what you want — reaching down is easier than reaching up, and the difference here is a foot. The one to watch is when the division lands just past a whole number: 25.5 feet of working height at five foot lifts pushes you to six lifts and thirty feet of platform for the sake of six inches, and that is a whole extra lift of frames, braces and possibly ties.
Everything this page will not tell you
It will not tell you whether the scaffold stands up. Not the base, not the bracing, not the plank spans, not the ties, not what the ties are fixed to, not the height it may be built to on that base width, not whether the ground under the bottom frames will hold it. Those figures exist, they are specific to the frame set and the situation, and they live in the manufacturer instructions and with whoever is competent to take responsibility for the scaffold in front of them.
The reason this page draws that line hard rather than offering a cautious estimate is that a wrong number here is not a wasted trip to the yard. Scaffold collapses and falls from scaffold kill people every year, and a materials list that quietly implied an arrangement was fine would be worse than no page at all. The count is useful for ordering and pricing. It is not a design.
For the tonnage that has to reach the platform once it is up, the masonry weight calculator gives the weight and the material hoist calculator gives the number of trips it takes. For access where a scaffold is not the answer, the ladder angle calculator and the boom lift reach calculator.
Questions people ask
How many bays of scaffold do I need for a wall?
Divide the run by the bay length of the frames you are getting and round up. A 48 ft wall with 7 ft bays comes to 6.857, so seven bays — six full and one six-foot part bay at the end. The count of frames is one more than the number of bays at each level, because bays share the frame between them.
How many planks fit across a scaffold bay?
Divide the frame width by the plank width and round up. A 5 ft walk-through frame is 60 in across and a nominal 2x10 scaffold plank is about 9.25 to 9.5 in wide, so seven planks — which overrun the frame slightly rather than fitting it exactly. Measure a plank rather than assuming the nominal size; aluminium and laminated decks are their own widths.
Does the short bay at the end of the run need fewer planks?
No, and this is the classic ordering mistake. The end bay is still a bay: it gets frames, braces and a full deck across its width, and the deck planks run the bay length rather than being cut to fit. Ordering planks off total square footage rather than off the bay count leaves you short every time the run does not divide evenly.
Can this tell me how high I can build the scaffold?
No. Allowable height depends on the base width, whether outriggers are fitted, what the scaffold is tied to, how it is braced, what it is standing on and what load it is carrying, and every one of those figures belongs to the specific frame set and situation. They come from the manufacturer instructions and from a person qualified to take responsibility for the scaffold. The ratio shown here is arithmetic on your two numbers and nothing more.
Why does the page ask me to enter the tie spacing instead of working it out?
Because there is no general figure to work it out from. Tie spacing depends on the frame system, the height, the base, whether the scaffold is sheeted or screened, wind exposure and what the ties are anchored into, and it is specified rather than derived. If you have been given a spacing, the page will turn it into a count of positions. It will not invent one, and it will not tell you whether a spacing is enough.