Door Handle Backset & PZ Sizing Guide

Aged Brass 3" 5 Lever BS Deadlock, from our current range.

Two measurements, easily confused

Backset and PZ are two of the most commonly confused measurements when ordering a door lock or handle set, but they measure two different things. Getting either wrong is one of the most common reasons a new lock does not fit an existing door.

What is backset?

Backset is the distance from the edge of the door to the centre of the keyhole or spindle hole. It determines how far into the door the lock sits, and is usually 44mm, 57mm, 63mm or 76mm on UK doors, with 63mm and 76mm being the most common on standard internal and external doors.

How to measure it: measure horizontally from the edge of the door to the centre of the existing keyhole or spindle hole. If you are fitting a new lock with no existing hole, this measurement is determined by the lock case you choose, not the door itself.

What is PZ (pin to centre)?

PZ, short for pin to centre, is the vertical distance from the centre of the spindle hole to the centre of the keyhole, on a lock that has both. This measurement is specific to sashlocks, which combine a latch with a key-operated lock, and is not relevant to a lock with only a spindle or only a key, such as a deadlock or a simple latch.

How to measure it: measure vertically from the centre of the spindle hole straight down (or up) to the centre of the keyhole. Common PZ sizes are 72mm and 92mm.

A worked example

If you are replacing an existing sashlock, measure the backset first (edge of door to spindle centre, commonly 63mm or 76mm), then measure the PZ (spindle centre to keyhole centre, commonly 72mm or 92mm). Ordering a replacement lock with matching backset and PZ measurements means it will line up with your existing door preparation without any further work.

Why this matters when ordering

• A lock with the wrong backset will not sit correctly within the door, or will not align with the existing mortice
• A lock with the wrong PZ will mean the handle and keyhole do not line up with your existing handle backplate or escutcheon
• If you are unsure, it is far easier to measure an existing lock accurately than to guess and risk having to re-cut the door

Related guides

See our Sashlocks and Mortice Locks guides, or browse our full Locks & Security Guide.

Frequently asked questions

What is the most common backset size in the UK?

63mm and 76mm are the two most common backset sizes on UK internal and external doors, though 44mm and 57mm are also used, particularly on older or narrower doors.

Do all locks have a PZ measurement?

No. PZ only applies to sashlocks, which have both a spindle-operated latch and a separate key-operated lock. A simple latch or a deadlock only needs a backset measurement.

What happens if I order the wrong backset?

The new lock will not sit correctly within the existing mortice cut into the door, and in most cases the door will need to be re-cut or a different lock ordered to match the existing preparation.

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