What Is a Backset?

If you’re fitting a new lock, latch, handle, or door knob, understanding the backset is essential. It affects how the door works, how comfortable the handle feels, and whether the hardware sits correctly on the stile. This guide explains what a backset is, how to measure it, and which size suits most UK doors.

Table of Contents

1. What Is a Backset?

2. How To Measure a Backset

3. Common UK Backset Sizes Explained

4. Backsets for Handles vs Door Knobs

5. Backset for New Doors vs Existing Doors

6. Matching Backset to Case Depth

7. Typical Problems Caused by the Wrong Backset

8. Conclusion

9. FAQ

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1. What Is a Backset?

 

The backset is the distance from the edge of the door to the centre of the spindle hole (for handles and knobs) or the centre of the keyhole (for locks).

Choosing the correct backset ensures:

• Comfortable hand clearance
• Correct alignment with the door stile
• Clean and professional hardware positioning
• Smoother, more natural operation

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2. How To Measure a Backset

 

To measure an existing door:

1. Locate the spindle or keyhole.
2. Measure from the door edge to the centre of that hole.
3. The measurement you get is the backset.

If replacing a lock or latch, match this size exactly to avoid reworking the mortice.

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3. Common UK Backset Sizes Explained

Backset	Typical Case Depth	Where It’s Used
44mm	64mm case	Narrow stiles, older properties, small lever handles
57mm	76mm case	Most modern lever handles
82mm	102mm case	Door knobs needing additional clearance
107mm	127mm case	Large door knobs; wide doors
130mm+	152mm+ case	Commercial or specialist doors
60–71.5mm	Varies	Often found on older or bespoke doors

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4. Backsets for Handles vs Door Knobs

Lever Handles

A 57mm backset works well for most lever handles. It gives comfortable spacing and avoids the handle sitting too close to the frame.

Door Knobs

Knobs sit closer to the door edge, so a deeper backset is usually needed:

• 82mm backset – best for most knobs
• 107mm backset – for larger or architectural knobs

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5. Backset for New Doors vs Existing Doors

Replacing a Lock in an Existing Door

Match the existing backset. This avoids:

• Re-routing the mortice
• Filling old holes
• Misaligned handle positions

Fitting a New Door

You can choose freely:

• 57mm for lever handles
• 82mm for door knobs
• 107mm+ for oversized knobs

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6. Matching Backset to Case Depth

Backset and case depth are not the same. Each backset corresponds to a typical lock case size:

• 44mm backset → 64mm case
• 57mm backset → 76mm case
• 82mm backset → 102mm case
• 107mm backset → 127mm case

Check both measurements when ordering hardware.

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7. Typical Problems Caused by the Wrong Backset

• Handle too close to the frame
• Knuckles catching the architrave when using a knob
• Furniture sitting off-centre on narrow stiles
• Extra drilling or widening required
• Uneven appearance on the door face

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Conclusion

A backset is a simple but essential measurement for fitting locks, latches, handles, and door knobs. The right size ensures comfort, correct spacing, and a clean installation. In most UK homes, 44mm and 57mm backsets cover the majority of lever handles, while 82mm and 107mm suit door knobs. Always measure your existing hardware, and choose the most suitable backset when fitting a new door.

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FAQ

What is a backset?

The distance from the door edge to the centre of the spindle or keyhole.

What backset is standard in the UK?

Most internal lever handles use a 57mm backset.

What backset should I use for door knobs?

Door knobs usually need 82mm or 107mm for comfortable spacing.

Is case depth the same as backset?

No. Case depth is the full body length; backset is the spindle/keyhole position.

Can I change from 44mm to 57mm?

Yes, but only if you are prepared to alter the existing mortice. Matching the existing size is easier.