How To Measure Locks

For a quick insight into the measurements you will come across when shopping for a new lock, read the tips we have outlined here...

The Case Depth - This is the depth that the lock goes into the door from the opening edge. With lever locks the two most common sizes in the UK are 64mm and 78mm. The best way is to quickly pop the old lock out and measure from the forend (the metal plate you see on the opening edge of the door when opened) to the back of the lock. This can also help you find a lock for a door that has already been morticed to accept a lock, but doesn’t have one fitted. Just take a ruler, insert it into the hole where the lock would normally be and take your reading. In most cases, it's safe to assume that it’s going to be somewhere between 64mm and 78mm.

The Backset – It's possible to take this measurement with the lock still in the door. The backset refers to the distance from the closing edge of the lock, to where the latch or deadbolt pops out. With a lever lock this is pretty straight forward because the keyhole is small enough to get a decent measurement, however, if you are measuring a euro or oval profile sash case that doesn’t have a cylinder fitted, things can get a bit complicated. If possible, measure the cylinder cavity at its widest point, divide this number by 2, then take a separate measurement from the locks edge to the start of the cavity and add the above figure on top.

The PZ – The PZ measurement is more commonly found in UPVC locks, gearboxes and handles. Whilst not always necessary (depending on your lock), it is important to take note. In its simplest form, the PZ measurement is the vertical distance between the centre of the keyhole and the center of the spindle that operates the latch in the sashlock. Only a sashlock can have a PZ measurement as a deadlock doesn’t have a handle spindle, latch or handles!