Sep 1, 2025
A Euro cylinder lock is a core component of a door’s locking mechanism, preventing unauthorised access and improving safety. Used on residential and commercial doors, including uPVC, composite, and aluminium doors, they are a popular choice due to their modular design, making them easy to replace and upgrade. Euro cylinder locks feature a key-operated cylinder that controls the locking mechanism, as well as a cylindrical barrel that houses the pins, aligning when the correct key is inserted and allowing the lock to turn.
There are various types of cylinder locks, designed for different access and security needs. Each type controls how the door can be operated from the inside and outside, offering varying levels of convenience and safety. Before you begin measuring for the correct size, you need to know what type is right for your needs.
A single cylinder lock, also known as a half cylinder, is a popular lock choice for doors where access is required from one side only. They are key-operated on one side of the door, with the other side left blank or inaccessible. Commonly used on doors in storage rooms and garages, these locks are easy to install and operate.
A double cylinder lock allows a key to operate the lock from both the inside and the outside, offering enhanced security for external doors. For those looking for maximum protection, these locks eliminate the possibility of the door being opened without a key from either side, making them a heavy-duty and premium choice.
A full thumb-turn cylinder lock features a key-operated lock on the external side and a thumb-turn knob internally. This allows for a quick and easy exit without a key, making these locks ideal for apartments and fire escape routes. Thumb-turn cylinder locks are robust and secure, popular due to their easy operation and high-quality design.
A half thumb-turn cylinder lock functions like a single cylinder lock, but includes a thumb-turn instead of a key on one end. These locks are used where internal locking and quick manual operation are needed, but external access is not, such as service cupboards and private internal zones. They offer a mix of security and convenience, making them an excellent user-friendly option.
Euro cylinders come in a variety of sizes to suit different door thicknesses and handle setups. Sizes are based on the measurement from the centre fixing hole to each end of the lock. By understanding the various sizes available, you can determine which is the best fit for your door.
Euro cylinders are measured from the centre of the fixing hole to each end, giving two numbers. These represent the lengths of the external and internal sides, which should be used to ensure the Euro cylinder fits the door and hardware correctly. Doing so will result in smooth operation and maintain security.
The overall cylinder length is the combined measurement of both sides (e.g. 40mm + 50mm = 90mm total). While getting the split measurement right is more important than simply matching the total length, uneven sides can affect both fit and function, so it’s essential to measure accurately from both ends to the centre fixing hole. To ensure proper alignment, choose a cylinder that matches your door’s requirements precisely.
An equal cylinder has the same measurement on both sides (e.g. 45/45), while an offset cylinder has different measurements (e.g. 35/50). Choosing between the two depends on the placement of the lock within the door and the thickness of the handles. Making the right decision ensures the cylinder sits flush and maximises security.
You’re now aware of the different Euro cylinder lock sizes, and you can begin to measure for the correct size for your door. This will enable you to make the right choice, fitting your specific needs and preferences. We will take you through a step-by-step measuring process to ensure your cylinder sits flush.
The first step involves locating the central fixing screw, which is usually visible on the edge of the door and directly level with the cylinder. It secures the cylinder in place and marks the central point from which both sides of the cylinder are measured.
You now need to decide whether to measure in or out of the door. The cylinder can be measured while it’s still in the door, but removing it yields the most accurate results. If you do decide to measure the cylinder off the door, you need to remove it by undoing the central fixing screw. To do this, insert the key, turn it slightly to align the cam, and gently slide the cylinder out.
Measure from the fixing hole to each end with a ruler or tape measure. You need to take two measurements, which include one from the centre of the fixing hole to the outer edge (external side), and one from the centre to the opposite edge (internal side). These measurements are usually unequal, so don’t panic if the numbers differ.
You now need to accurately identify the internal and external sides, labelling each measurement correctly. The external side is the one that faces outside of the building, which is especially important to note with any cylinder lock types with a thumb-turn or any other configuration.
Recording the correct size format is important, as Euro cylinders are measured in two parts, which include from the centre of the fixing hole to each end. Sizes are typically written as two numbers (e.g., 40/50), representing the external and internal lengths in millimetres. You should always double-check which side is which, as some suppliers list the external side first. Once recorded correctly, you’ve successfully measured your Euro cylinder and are ready to choose a suitable replacement.
This guide has taught you how to measure the correct cylinder lock sizes, the various types and sizes available, and which is best suited to you. Find the right lock required for your next project with our wide range of cylinder door locks at IronmongeryDirect.
Measure from the centre of the fixing screw hole to each end of the cylinder, both external and internal sides. Removing the lock helps ensure accuracy, but you can also measure while installed by locating the fixing screw on the door edge.
No, not all Euro cylinder locks are the same. They can vary in length, type (single, double, thumb-turn), and security features. Their sizes and functionalities are designed to suit different door thicknesses and security needs
Yes, you can replace a Euro cylinder lock yourself if you have the basic tools and confidence to do so. If you’re unsure, you should reach out to a professional to ensure that the replacement is installed properly and works effectively.
The most common size is typically 35/35mm or 40/40mm, which suits standard door thicknesses. However, many doors require offset sizes depending on the door and handle configurations.
You will need a tape measure or ruler for measuring, a screwdriver to remove the fixing screw, and the correct replacement Euro cylinder lock. Having the correct tools will ensure the process runs smoothly.
In order to know if your Euro cylinder lock is secure, you need to check for security features like anti-snap, anti-pick, anti-drill, and anti-bump protection. Certification standards such as TS007 (3-star rating) indicate high-security locks.
