What Is Backset on a UPVC Door Lock? Explained Simply

Introduction

Backset is one of the most important measurements when replacing a UPVC multipoint door lock. Ordering the wrong backset will result in poor handle alignment and incorrect door function.

This guide explains what backset means and how to measure it correctly.

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What Is Backset?

Backset is the distance from:

• The edge of the door
  to

• The centre of the spindle hole

It determines how far the handle sits from the door edge.

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Common UK Backset Sizes

• 35mm (very common)

• 45mm

• 55mm

Always measure your existing lock before replacing.

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How to Measure Backset

1. Open the door.

2. Locate the faceplate (metal strip on door edge).

3. Measure from the outer edge of the faceplate to the centre of the spindle hole.

4. Record the measurement in millimetres.

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Why Backset Matters

If the backset is incorrect:

• The handle will sit too close or too far from the edge.

• The lock may not function correctly.

• The door may not secure properly.

Correct measurement ensures proper fit and security.