How Many Locks Can Be Put on One Master Key System?
A six pin cylinder platform can support several hundred distinct change keys under a single master, and commercial platforms with seven pins or side bars extend into the thousands. In practice most residential and small commercial systems use between three and fifty cylinders, well within any platform's capacity. The real limit is not the number of locks but the number of distinct access levels required and the security cost of adding master wafers to every chamber.

The question of how many locks a master key system can hold usually comes from someone planning ahead — a
landlord acquiring more properties, a business expanding into an adjacent tenancy, a strata committee considering whether one system can cover a whole building. The reassuring answer is that the practical ceiling is far higher than most people need. The more useful answer is that system size is rarely the constraint. Design is.
What Determines Capacity
Pin count.
Each pin chamber in a cylinder can be cut to a range of depths, typically between five and ten distinct positions depending on the manufacturer. The total number of possible key combinations is roughly the number of depths raised to the power of the number of pins. A six pin cylinder with seven usable depths yields well over a hundred thousand theoretical combinations.
Master wafers reduce the usable total.
Adding a master wafer to a chamber creates a second valid position in that chamber, which consumes combinations. Every level of hierarchy consumes more. A system with a grand master, sub-masters, and change keys uses a meaningfully larger share of the available combination space than a simple two-level system.
Manufacturer keying rules.
Platform manufacturers publish rules on which combinations can coexist safely in a system, preventing situations where one change key accidentally operates another door. These rules reduce the theoretical maximum to a practical one, which is still comfortably in the hundreds for a standard six pin platform.
Typical System Sizes
Residential.
Three to eight cylinders covering external doors, a garage, and perhaps a garden gate or shed. Well within any platform.
Landlord with multiple properties.
One key per tenancy plus a management master across all of them. Even twenty properties with four doors each is eighty cylinders, which a standard commercial platform handles without difficulty.
Small commercial premises.
Six to twenty cylinders with two levels of hierarchy. Routine.
Apartment or strata building.
Individual tenancy keys, common area access, a building manager master, and contractor access to plant rooms. This is where hierarchy depth matters more than lock count, and where design quality determines whether the system works.
The Real Constraints
Hierarchy depth, not lock count.
A system with fifty cylinders and two access levels is simpler than one with fifteen cylinders and five access levels. Each additional level multiplies the master wafers required and complicates the design.
Security cost of master wafers.
Every master wafer creates an additional shear point in the cylinder, which marginally reduces resistance to picking and manipulation. A cylinder with wafers in every chamber is measurably easier to manipulate than one keyed to a single key. Good design places wafers in as few chambers as the hierarchy allows.
Future expansion.
A system designed to exactly fit today's doors leaves no combinations in reserve. Adding doors later then requires either a partial redesign or accepting combinations that sit outside the original logic. Reserving capacity at the design stage costs nothing and saves considerable work later.
Key control across the system.
The larger the system, the more consequential a lost master key becomes. A grand master covering eighty cylinders that goes missing means eighty cylinders to rekey. This is the strongest argument for building large systems on
restricted key profiles.
Designing for Growth
A locksmith designing a master key system should ask what the system needs to cover in five years, not just today. For a landlord, that means asking whether more properties are likely. For a business, whether adjacent tenancies may be taken on. For a strata building, whether additional common facilities are planned.
Reserving combination capacity for that growth is a design decision made once, at the beginning, and it determines whether future expansion is a simple addition or a system rebuild.
Frequently Asked Questions
Can one master key open locks in different buildings?
Yes, provided all the cylinders are on the same platform and were designed into the same system. This is standard for landlords with multiple properties and for organisations operating across several sites.
What happens if we outgrow the system?
If capacity was reserved at design, additional cylinders are simply keyed into the existing system. If not, the locksmith may need to redesign the hierarchy, which can require rekeying some or all existing cylinders. This is why the growth question matters at the outset.
Does a bigger system mean weaker security on each lock?
Not directly from size, but from hierarchy depth. More access levels mean more master wafers per cylinder, and more wafers mean marginally reduced manipulation resistance. Keeping the hierarchy as shallow as the access requirements allow is good practice.
Can we have more than one master key level?
Yes. Grand master, sub-master, and change key is a common three-level structure. Larger organisations use more. Each level should exist because a real access requirement demands it, not because the structure looks tidy.
How long does it take to install a system across many doors?
Design is typically a matter of days. Installation runs at roughly fifteen to thirty minutes per cylinder depending on hardware type, so a fifty cylinder system is several days of on-site work, usually scheduled around access availability.
Contact Malvern Lock Service on 0477-615-507 for master key system design and installation across Melbourne's inner south-east. Neale designs key hierarchies with expansion capacity built in, for homes, rental portfolios, strata buildings, and commercial premises. Over 35 years of experience. MLAA member and VIC Police registered. Serving Malvern, Malvern East, Armadale, Toorak, Prahran, South Yarra, Glen Iris, Camberwell, Glen Huntly, Hawthorn, Kooyong, St Kilda, St Kilda East, and Surrey Hills.