Euro Cylinder Lock Sizes Explained: How to Measure Yours

Euro cylinder locks come in many different sizes, and getting the right size is essential for both security and function. If the cylinder is too long, it protrudes from the door and becomes an easy target for snapping. If it's too short, it won't engage properly with the thumb turn or key on the other side.

To measure your euro cylinder, you need to remove it from the door. Insert your key and turn it slightly (about 15 degrees) so the cam (the metal tongue on the back of the cylinder) is aligned with the body of the cylinder. Then undo the fixing screw — this is usually located on the edge of the door, level with the cylinder. You can then pull the cylinder out.

With the cylinder removed, measure from the centre of the screw hole to each end. You'll get two measurements — for example, 35mm on the outside and 35mm on the inside (written as 35/35). These two numbers might be different — for instance, 40/35 or 45/40. The longer side usually faces outward.

When choosing a replacement, the cylinder should sit flush with or slightly recessed from the door hardware on both sides. A cylinder that protrudes more than 3mm from the handle or escutcheon is vulnerable to snapping attacks.

If this all sounds complicated, don't worry — your locksmith will measure and select the correct size for you. At Oldham Locksmiths, we carry a range of common sizes in our vans and can source any unusual sizes within 24 hours. Call 07949 139 475 for assistance.