// Hardware Basics
5 min read
Key Charts Explained:
How Master Key Systems Work
A "key chart" (or keying chart) is the map that shows how the keys in a building relate to each other — who can open what. It's the backbone of any master key system, and understanding it makes ordering replacement keys and locks far less confusing.
The three levels
Change key
Opens one specific lock, and only that lock. This is what most people think of as "a key."
Master key
Opens every lock within a defined group (say, all offices on one floor), even though each of those locks also has its own unique change key. One person carries the master; everyone else carries only their own change key.
Grand master key
Sits above multiple master key groups and opens everything in the entire system — every master group and every individual lock underneath it. Typically held by a facilities manager or building owner.
Picture it like an org chart: the grand master key sits at the top, master keys branch out to cover specific groups of doors, and each door still has its own individual change key underneath its master.
Why this matters when ordering
- Every lock in a master key system is cut to accept two different keys: its own change key, and the master key above it. This means the internal pinning is more complex than a standalone lock, so master-keyed locks generally cost more and take longer to key.
- Adding a new lock to an existing system isn't as simple as buying any lock off the shelf. It has to be cut to match the existing master key chart, which usually means going through the locksmith or supplier who holds your chart on file — not just any hardware store.
- Key charts are typically confidential and factory-controlled. Reputable suppliers won't cut keys against someone else's chart without proof of authorization, since doing so would undermine the whole point of the system.