How to Measure a Cylinder Lock?

Measure half a loose cylinder

A half cylinder can be operated from one side with a key. The cylinder is measured from the center, the center of the bolt hole. The blind side (the side that is not used) is always 10 mm. The dimensions of a half cylinder are therefore indicated as, for example, 30/10. This means that the side used is 30 mm and the other side is 10 mm. This makes the total length 40 mm.

Measure a cylinder of a cylinder lock that is still in the door

Finally, it may also happen that you want to measure a cylinder lock that is still attached to the door. You start by measuring from the center of the cylinder locking screw (see image). This is the first screw under the deadbolt. Then measure the distance to the left where the door fitting is attached. Add the thickness of the door fittings on this side. You also do this for the right side.

For example:

• The distance to the left side is 20 mm + thickness of the door fitting is 8 mm = total 28 mm.
• The distance to the right side is 20 mm + the thickness of the door fitting is 20 mm = 40 mm.

A cylinder is always at least 30 mm long and, according to the Police Quality Mark for Safe Living, may not protrude further than 3 mm from the fitting. The length of a cylinder can be increased in steps of 5 mm.

In the example you need 30 mm on one side (this only extends 2 mm from the fitting) and 40 mm on the right side. This amounts to a size of 30/40.

Anyone can learn how to measure a cylinder lock, and it is not very difficult. If you still have questions, call or app the Door Hardware Expert Lock Specialist .