Where the capacity comes from
Only the progressed chambers do any work. A chamber held at the master depth in every cylinder in the building is the same cut on every key, so it separates nothing. If four chambers of a six-pin cylinder are progressed, the system is a four-digit number in whatever base the usable depth set gives you.
The base is the part people get wrong. Ten depths on the chart with a two-step progression does not give ten usable positions, it gives five — depths 0, 2, 4, 6 and 8. So four progressed chambers is five to the fourth, 625 patterns, one of which is the top master key itself. That is 624 change keys if the system is flat.
Two levels cost you more than the chamber
Split those four chambers two and two and the arithmetic changes shape. The master level holds 5 squared less one, 24 master groups; under each of them the change level holds 5 squared less one, 24 change keys. Twenty-four times twenty-four is 576 — against 624 for the flat system. Giving the system a middle layer cost 48 positions, and it bought a key that opens a whole department.
Push the split further and it costs more. Three chambers to the master level and one to the change level is 124 masters at 4 keys each, 496 positions. The lopsided splits are always the expensive ones, which is worth knowing before somebody promises a tenant their own sub-master.
The adjacent cut rule is not a rounding error
The maximum adjacent cut spec caps how far two neighbouring chambers can differ. On a six-chamber cylinder drawing from a five-depth set with a spec of 7, 10,727 patterns out of 15,625 survive — about 69 percent. Tighten the spec to 4 and it falls off a cliff. The page prints this as a whole-cylinder figure rather than folding it into the capacity, because turning it into a count of your keys needs the bitting list, and asking for one is exactly the thing this page will not do.
What the numbers cannot tell you
Capacity is arithmetic; a system is a policy. How many people carry a master, who can cut a blank, what happens when somebody leaves — none of that shows up here, and all of it decides whether the system is worth having in five years. Sizing the reserve is the one piece of policy the form does touch: the default holds 40 positions back, and a building that hands out every position it has is a building that starts over the first time a floor gets subdivided.
If the count comes up short, the fix is a system design conversation with the cylinder manufacturer or a door hardware consultant, not a bigger number in a box. Related pages: the door hardware schedule calculator for the counts that go with the openings, and the building rekey inventory calculator for what actually gets bought when the system changes.
Questions people ask
How many change keys does a six-pin system hold?
It depends entirely on how many chambers are progressed and how big the progression step is, not on the six. Four progressed chambers off a ten-depth chart at two-step gives 625 patterns and 624 change keys flat; split two and two into masters and changes and it gives 576. Progress only three chambers and the same chart gives 124. The chamber count sets the ceiling and the progression sets what you actually get.
Why does a two-step progression halve the depths?
Because a two-step progression only uses every other depth number. Ten depths numbered across the chart gives 0, 2, 4, 6 and 8 — five usable positions per progressed chamber instead of ten. The reason for leaving the gap is a manufacturing and wear question for the cylinder maker, and this page takes your step as given rather than recommending one.
Does this tell me what my keys are cut to?
No, and it is built so it cannot. The form takes counts only — how many chambers, how many depths, how big the step. There is no field for a bitting and no output that is a key cut. Producing an actual keying schedule means assigning bittings to doors, and that is work for the cylinder manufacturer or the locksmith who holds the system chart, who keep the list controlled for the obvious reason.
What is MACS and why does it cut the count down?
The maximum adjacent cut spec is the largest difference the chart allows between two chambers sitting next to each other, and it exists because a very deep cut beside a very shallow one is hard to cut cleanly and hard for a cylinder to read. Every pattern that breaks it drops out. On a six-chamber cylinder drawing from five depths at a spec of 7, roughly a third of the patterns go, which is a bigger bite than most people expect from a rule that sounds like a detail.
How much reserve should the system keep?
That is a building question rather than an arithmetic one, and the field defaults to 40 as a placeholder to replace. The thing worth planning for is subdivision: a floor that becomes two tenancies needs a new master group and a fresh run of change keys, and a system with no unassigned positions cannot supply either without rekeying something that already works.