A lever-tumbler lock uses a stack of gated, spring-biased levers. The correct key moves every gate into one common channel so the bolt fence can pass. The calculator counts nominal discrete position combinations; it does not measure resistance to picking or forced entry.
Lever Tumbler Lock Interactive Calculator
Vary the number of independently assigned levers, the declared positions per lever and a user-declared exclusion count. The result is a nominal combinatorial space, not a security grade or key-duplication probability.
Equation Used
- The L lever positions are labelled and independent in the nominal count.
- Every position has exactly D declared discrete settings before exclusions.
- Security performance, picking resistance, manufacturing feasibility and accidental interchange are not inferred.
The nominal combination count assumes independent lever settings. A product’s usable key combinations and security performance depend on its mechanical design, keying rules and testing.
How gated levers control the bolt
In a conventional lever-tumbler lock, each spring-biased lever pivots and carries a gate. A fence or stump associated with the bolt cannot move through the lever pack while any gate is out of line. The correct bitted key raises the levers by different amounts until all gates form one channel, allowing the fence and bolt to move.
The animation is an exploded phase diagram with rigid pivoted lever plates: prescribed key motion brings the gates into alignment, bolt-fence travel occurs only while alignment is held, and the bolt returns before the levers lower. The key profile, springs and layer spacing are explanatory, not a manufactured lock layout or attack simulation.
What the count can and cannot show
The calculator evaluates a simple labelled-position count. It is useful for checking arithmetic when a design explicitly declares L independent positions and D available settings at every position.
It does not establish usable key differs for a product. Actual systems may prohibit adjacent steps, reserve settings, repeat keys, use master-key relationships or lose distinctions through tolerances. A security rating also depends on construction and attack testing, not code-space size alone.
Nominal discrete position space
There are D choices at each of L labelled lever positions, so the multiplication rule gives D×D×…×D = DL. With a user-declared exclusion count R:
The displayed information count is log₂(Kuse) when at least one assignment remains. If Kuse is zero, log₂(0) is undefined and the output is unavailable—not zero bits. These are mathematical counts, not measured security.
Worked counting example
For five labelled lever positions and five declared settings per position, the nominal space is 55 = 3,125 assignments. If the user declares 625 assignments excluded, 2,500 remain and the information count is log₂(2,500) = 11.3 bits.
The example does not claim that a particular lock manufacturer permits those assignments or that all surviving keys are mechanically distinct.
Limits of a code-space count
Increasing L or D expands the nominal mathematical space exponentially. It can also increase mechanical complexity and introduce product-specific restrictions that this calculator does not know.
No conclusion about picking, impressioning, destructive attack, accidental interchange, certification, insurance acceptance or safe installation follows from DL.
Lever-lock counting questions
Does the result equal a manufacturer's published key differs?
No. It equals a declared independent-position model after a user-entered exclusion count. Manufacturer keying rules are not supplied.
Does more entropy mean a lock is secure?
Not by itself. The bit count only restates the size of this abstract assignment set. Security requires physical design and attack evaluation.
Why do all gates have to align?
The bolt fence must pass through every lever gate. One misaligned lever blocks the fence.
Primary mechanism reference
- GB 2480089 A, Lever tumbler lock with blocking means: describes spring-loaded pivoted levers, gates, a bolt fence and key-controlled simultaneous gate alignment.
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