How to Measure a Euro Cylinder Lock: A Simple UK Guide

Replacing a euro cylinder starts with getting the size right. Whether your lock is fitted to a uPVC, composite or timber door, a few careful measurements can help you choose a suitable replacement.

What is a euro cylinder?

A euro cylinder is the removable key-operated part of many modern door locks. It sits inside the door and operates the locking mechanism. Cylinders are available in different lengths, finishes and security ratings, including key-and-key and key-and-thumbturn options.

Measure from the fixing screw

Euro cylinders are normally described by two measurements: the distance from the centre of the fixing screw hole to one end (A), and the distance from the centre to the other end (B). For example, a 35/45 cylinder measures 35 mm on one side and 45 mm on the other, giving an overall length of 80 mm.

1. Open the door and locate the long cylinder retaining screw on the door edge, roughly level with the keyhole.
2. Measure from the centre of that screw to the outside face of the cylinder or its intended finished position.
3. Measure from the same centre point to the inside face.
4. Record both measurements and which side faces outside. For thumbturn cylinders, the orientation matters.
5. Check that the replacement will sit appropriately within the door furniture and follow the cylinder manufacturer’s fitting guidance.

Should a cylinder stick out?

A cylinder that projects too far beyond the external handle or escutcheon can be more vulnerable to attack. Choose a correctly sized product and compatible security furniture. Avoid assuming that overall length alone tells you the correct size: the split matters.

What about anti-snap cylinders?

For external doors, consider a cylinder with an independently verified security rating, such as a TS 007 three-star cylinder, or a suitable combination of cylinder and protective door furniture. Check the current certification and the manufacturer’s installation instructions rather than relying only on marketing terms.

Common measuring mistakes

• Measuring the full door thickness without allowing for the handles or escutcheons.
• Recording the total length but not the two separate sides.
• Ordering a thumbturn cylinder with the thumbturn on the wrong side.
• Choosing a cylinder that projects unnecessarily beyond the external furniture.

Shop locks and door hardware

Explore our euro cylinders at Lockora. If you are unsure about sizing, check your existing cylinder and door furniture before purchasing. If the door still will not lock correctly, our multipoint gearbox guide explains other possible causes. For local fitting and repairs in Dundee, visit Locksmith Dundee.