Master Key Chart: How to Read and Draw One, With a Worked Example

A master key chart answers two questions about a building in one table: what does each key open, and which keys open each door. Keys run down the side, doors run across the top, and a cross marks every place a key works. Read along a row and you have everything one key opens; read down a column and you have every key that opens one door. The second reading is the one people need on the day a key goes missing.

This page draws a chart for a small three-level system, explains how to read it, gives five steps for drawing one for your own building, and ends with a blank chart to print. The symbols follow the convention most North American keying schedules use, from the Door and Hardware Institute's handbook Keying Systems and Nomenclature. How many levels a building needs, and why each level costs key capacity, is covered in our article on master key levels.

Three documents, one building

A master key system is described by three tables that share door numbers, and they are easy to confuse because all three get called a chart. The key chart is the one on this page: keys against doors. The keying schedule lists cylinders, one row per cylinder, and the cylinders are pinned from it. The key list records the physical keys: every copy that was cut and who holds it. The chart comes first, because the schedule and the list are both read off it.

The symbols, in one paragraph

Letters are master keys and numbers are change keys. In a two-level system the master is AA and the change keys put their number first: 1AA, 2AA, 3AA. In a three-level system the grand master is one letter, A; the masters under it take two letters, AA, AB, AC; and the change keys put the number last: AA1, AA2, AB1. A four-level system adds a great grand master, GGM, above grand masters A and B. A cylinder that no change key opens carries the symbol of the master that does, so a room opened only by master AB and the grand master is written AB. An X in front of a symbol, as in XAA2, marks a cross-keyed cylinder: one also opened by a key from another branch.

A worked example: a two-floor clinic

Take a small clinic with eight lockable doors. The ground floor has reception and two consulting rooms; the first floor has an office, a records room and a staff room; the basement has a plant room and a cleaner's store. The owner wants one key for everything. The practice manager runs the ground floor, the office manager the first floor, and a maintenance contractor needs the service rooms and nothing else. That is three levels: grand master A, three masters, and change keys under each.

Across the top, 101 is reception, 102 and 103 the consulting rooms, 201 the office, 202 records, 203 the staff room, 001 the plant room and 002 the cleaner's store. Use the door numbers on the drawings rather than room names, because the same numbers have to appear on the keying schedule and on the hardware schedule.

How to read it

Read a row to check a person. The AB row has crosses on 201, 202 and 203 and nowhere else, which is exactly what an office manager should open. A cross in a row that its holder has no business with means the chart is wrong, and it is far cheaper to fix on paper than in brass.

Read a column to check a door. Column 202 has two crosses, A and AB, and no change key: nobody below the office manager opens the records room, which is why its cylinder is written AB. Every other column has three crosses, the grand master, one master and one change key. That is the normal shape of a column in a three-level system, and a column that departs from it is the one to look at.

Read the bottom line to see the load on each cylinder. The number of keys that open a door is the number of keys its cylinder must accept, and each key beyond the change key generally needs extra splits in the pin stacks. A column with crosses from two masters is a cross-keyed cylinder. It should carry an X in its symbol and a note naming both keys, and it is the first column to question, because cross-keying uses capacity the rest of the system may need.

Read a row again when a key is lost. Lose AB and its row lists what is exposed: 201, 202 and 203, three cylinders to recore and one master to recut. Lose A and every door in the building is exposed, which is why the chart gives the grand master the fewest copies, and why the key list should say exactly where each copy is.

The same building as a tree

Many charts are drawn as a tree instead of a grid: the top key at the head, a branch for each master, a leaf for each change key. A tree shows the hierarchy at a glance and hides the door numbers, so it makes a good cover sheet and a poor working document. Written as a table, the clinic's tree reads:

If the clinic did not need a master per floor, the same doors would make a two-level system: one master, AA, and change keys 1AA, 2AA and onward. The grid is drawn the same way, with one master row instead of three. A four-level system adds a great grand master row at the top, GGM, with a cross in every column, and a second grand master, B, with masters BA and BB under it.

We build master key systems of up to five levels. Above four levels the DHI handbook leaves the symbols to the manufacturer, so a five-level chart has to carry its own legend, written on the sheet, before anyone can read it.

Drawing one for your building

Five steps, in this order. First, write every door that takes a cylinder across the top, using the numbers on the drawings. Second, write every person or role that holds keys down the side, and next to each one what they must open. Third, group the doors that the same people open: each group becomes a master, and groups that answer to the same manager sit under one grand master. Fourth, assign symbols from the top down, letters for masters and numbers for change keys. Fifth, mark the crosses, count every row and every column, and look for the exceptions: a door with crosses from two masters, a door with no change key, and a change key with crosses in two columns, which means those two cylinders are keyed alike.

Before the chart goes out, check it against capacity. How many masters and change keys one level can hold is worked out in our article on master key levels; the short version is that the number of masters and the size of the largest group have to be settled together, and the chart is where both are visible. Then date the chart, give it a revision number, and keep it with the keying schedule. A chart that disagrees with the schedule is worse than no chart, because both look authoritative.

A blank chart to print

The sheet attached to this article is the same grid on one landscape page: sixteen door columns, twenty key rows, a header for the project, keyway, levels in use and revision, and the clinic example on the second page. Print it, or use your browser's Save as PDF. For a handful of doors, the table below can be copied straight into a spreadsheet.

What to send us

Send the chart, or the door list and who needs what if the chart is not drawn yet, together with the keyway the system should use and the door thickness at each cylinder. Our euro profile cylinders, such as the 60 SNDK, 54 SNDK and 90 SNDK, published with double key function, and the 80 SNKT, are pinned to the symbols on the chart, and the keying schedule that comes back carries the same symbols, so the two can be checked against each other line by line. A system is drawn for one building, and we would rather question a cross on paper than ship a cylinder that opens a door it should not.