Backset for Furniture Locks: Definition and Measuring Guide

The backset on a furniture lock refers to the exact distance from the centre of the keyhole or cylinder to the front edge of the lock. This measurement is given in millimetres and is crucial for ensuring that a replacement lock fits precisely into the existing hole of the furniture door or drawer.

What exactly is the backset?

The backset defines the position of the locking mechanism on the furniture front. It indicates how far the keyhole is located from the edge of the door. When installing a surface-mounted lock or a mortice lock, this value determines where the wood drill bit must be positioned. If the measurement on a replacement lock does not match the existing drill hole, the key cannot be inserted into the cylinder. The backset functions like the exact geographic coordinate of the mechanism – if it deviates by even one millimetre, the locking bolt will miss its mark.

Typical measurements in furniture manufacturing

In contrast to room doors, which often feature a measurement of 55 mm, the dimensions in furniture construction are significantly more compact. Typical values for a furniture lock range from 15 mm - 40 mm.

Standard incremental dimensions are:

• 15 mm
• 20 mm
• 25 mm
• 30 mm
• 40 mm

Types of furniture locks and their characteristics

Depending on the piece of furniture, different locking mechanisms are used where the backset is relevant:

• Surface-mounted lock: Screwed onto the inside of the door or drawer. Very common on classic chests of drawers and cupboards.
• Cylinder lock: A modern furniture cylinder lock is frequently fitted in office furniture or mobile pedestals.
• Espagnolette lock: Used on tall doors to lock them at multiple points. A cabinet lock with rods requires the correct rod lengths in addition to the correct backset, making it an essential wardrobe accessory.

Guide: How to measure the backset correctly

To determine the correct dimension for a replacement lock, the old lock is measured.

Required tools:

• Vernier calliper (recommended for precise millimetre readings) or a folding rule
• Screwdriver (drive PZ or TX) for disassembly

Step-by-step instructions:

1. Remove the lock: Loosen the wood screws and remove the lock from the furniture front.
2. Target the reference point: Place the measuring tool against the front edge of the lock case – this is the side from which the bolt extends.
3. Determine the distance: Measure from this edge precisely to the centre of the keyhole or the cylinder pin.
4. Read the value: Note the measurement in millimetres. If the value is 25 mm, for example, you strictly require a new lock with a backset of 25 mm.

Application and selection in furniture installation

When restoring or repairing furniture, the new lock must be selected with a precise fit to avoid complex woodwork or unsightly double drill holes on the front. In addition to the locking mechanism, functional and aesthetic components often play a role during replacement. If the cabinet door no longer sits straight within the carcass and causes the lock to jam, the concealed hinges / cabinet hinges should be adjusted or replaced.

Cabinet handles or drawer handles (wall unit handles) are also frequently chosen to match the cylinder rose of the new lock when overhauling the furniture front, creating a harmonious overall appearance.

Related terms

• Forend dimension: The length and width of the faceplate on a mortice lock.
• Striker plate: The counterpart to the lock, which is mounted on the furniture carcass and receives the bolt.
• Cylinder diameter: The outer diameter of the lock cylinder, which determines the required drill hole diameter (often 19 mm or 22 mm) in the door.