Enter your observations
Use measurements you can verify. Unknown or unreadable details can be left unspecified where the tool allows it.
Compare the existing cut-out with one replacement lock. Measurements below are in millimetres; use the edge of the door or drawer as the reference plane.
Existing opening / hardware
Replacement specifications
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How to use this tool
- Measure backset from the relevant door or drawer edge to the keyhole or spindle centre.
- Measure the existing mortise and faceplate independently.
- Enter replacement measurements from a supplier drawing or the actual lock.
- Review each difference and verify keyway, screw locations, throw and function before installation.
What the result means
A lock must fit the available mortise and place its keyhole or spindle in the correct position. Backset is a specific reference measurement; lock-body depth, width and height describe different dimensions and should not be substituted for one another.
The tool compares six dimensions against your tolerance and identifies whether the stated dimensions broadly align. It cannot assess the mechanism, lock throw, key profile, door thickness, fastener locations or whether installing the lock would remove historic material.
Limits and good practice
Antique lock dimensions may be stated differently by suppliers. Always read their dimension diagram carefully and confirm whether values refer to the case, faceplate or keyhole centre. Do not force a lock into a tight opening or cut original furniture before confirming compatibility.
References and further research
Frequently asked questions
Where is the backset measured from?
From the relevant door or drawer edge to the centre of the keyhole or spindle, following the measurement convention for the specific lock.
Can a matching backset alone prove fit?
No. The body, mortise, faceplate, fasteners and mechanism also need to fit.
Why compare faceplate dimensions separately?
The faceplate covers the edge opening and has its own height and width; it is distinct from the internal lock case.
What tolerance should I enter?
Base it on measuring accuracy and the manufacturer’s documented fit. A tolerance is not permission to force a component.
Can the tool tell if the old key operates the replacement?
No. Keyway and mechanism geometry must be compatible, and dimensions alone cannot guarantee operation.
Should I enlarge an antique mortise if the lock is close?
Pause and assess conservation impact first. Use a qualified furniture conservator or locksmith for valuable original furniture.