Home Improvement

Measuring Cylinder Locks: Tools, Steps, and Expert Advice

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When it comes to securing residential properties, you’ll find cylinder locks in countless modern homes, schools, hospitals, and businesses. They’re very versatile and easy to install since you don’t have to remove any other fittings on the door. But to install or replace one yourself, you first need to know the proper measurements.

In this blog post, you’ll become familiar with the essential tools, and all the other information on how to measure cylinder locks for your lock replacement or upgrade. So, say goodbye to guesswork and hello to precision!

Cylinder lock specifics you need to know

Cylinder locks, including euro cylinder and oval cylinder locks, are a combination of a keyhole and a tumbler mechanism contained within a cylinder, hence the name. Like any other lock, these work by using a key to align pins inside the lock mechanism, allowing the lock to turn and either secure or release the door.

As far as specifics regarding measuring, two things are important to you:

  1. Length – The overall length of the cylinder lock impacts the measurement and its compatibility with the door or device it is intended for;
  2. Diameter – The diameter of the cylinder affects its fit within the lock mechanism and is a crucial measurement.
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Are all cylinder locks the same size?

No. Cylinder locks come in various sizes to accommodate different types of doors and door frames. The standard sizing of a cylinder lock involves measuring the cylinder from the centre of the screw hole to each end. The measurements are always done in millimetres.

Cylinder locks are typically specified with two measurements separated by a forward slash, such as “30/30” or “40/40.” These measurements represent the total length of the Euro cylinder lock. For example, a “30/30” Euro cylinder lock has a total length of 60 millimetres, with 30 millimetres on one side (interior or exterior) and 30 millimetres on the other side.

How to correctly measure cylinder locks

Getting the right size for your cylinder lock is of utmost importance. If it’s too long, it can compromise your security because it will literally tick out of the mortice. The maximum length at which it can stick out and not pose a security risk is 5mm. Any longer than that and it will be easy to be broken via lock snapping. On the other hand, if the lock is too short, you’ll face difficulties in turning the key effectively.

Usually, you don’t need to measure the height or width of the lock. “Euro profile” is the industry standard, and all doors meant for such locks will have a mortice with the same diameter and height. It’s the length of the lock that matters in most cases unless you have a lock that’s very different in size compared to the majority. With all said so far, this is what you need…

Required Tools:

  • Measuring tape or ruler
  • Screwdriver
  • Calipers (for precise diameter measurement)
  • Paper and pen (for note-taking)

Step 1: Determine the type of lock you have

Examine the lock on your door visually. Pay attention to the shape and features of the keyway and the lock itself.

  • Euro cylinder locks Euro cylinder locks have a cylindrical shape with a keyway that extends through the centre of the lock. They are commonly found in uPVC and composite doors;
  • Oval cylinder locksOval cylinder locks, as the name suggests, have an oval shape. They are often used in vintage or antique doors and may have a keyway located on one side of the oval;
  • Thumbturn/Single cylinder locks – These locks typically have a keyway on one side and a thumbturn or knob on the other side for easy locking and unlocking from the inside without a key;
  • Double-cylinder locks – Double-cylinder locks have keyways on both sides of the door, requiring a key for entry and exit.
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Step 2: Remove the cylinder lock from the door

Now, it is quite possible to measure the door cylinder while it’s still in the door, however, it will be much easier and you will have more certainty when it’s out of the lock.

Use the appropriate screwdriver to loosen and then fully remove the retaining screw. With the screw removed, insert the key into the cylinder lock and turn it until the cam (the part that protrudes from the lock) goes back into the lock.

Once the cam is retracted, you can now carefully slide or pull the cylinder lockout of the door. If it’s a tight fit, you might need to use pliers to grip and gently wiggle the lock free.

Be cautious not to force it, as this can damage the lock or the door.

Step 3: Measure the length

The measurement for all types of cylinder locks should typically be taken from the centre of the screw hole to the outer edge of the cylinder on both sides. This method ensures that you get the total length of the cylinder.

This also means that the measurement process is generally the same for euro cylinder locks, oval cylinder locks, thumbturn/single or double cylinder locks, and other cylinder lock types.

When you have a thumbturn lock, do not measure the thumbturn, only to the barrel end.

Step 4: Take measurements of the cylinder’s diameter

For Euro cylinder locks and thumbturn/single cylinder locks, measure the diameter of the cylinder, which is often referred to as the thickness. You can use a calliper or measuring tape to obtain this measurement, if necessary.

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Step 5: Measure the cam length

The cam is the protruding part of the cylinder that interacts with the locking mechanism. You will hardly need to measure this, but it’s still good to know just in case.

  1. For Euro cylinder locks – Measure the length of the cam, which is typically the distance from the centre of the screw hole to the tip of the cam.
  2. For double cylinder locks – Measure the length of both cams, as they can be of different lengths.

These measurements are essential to ensure that your new lock will fit correctly. Be precise and double-check your measurements, as small errors can lead to installation problems or security vulnerabilities.

Need a professional locksmith's help?

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Need a professional locksmith's help?

Get in touch with local locksmith.

Learn more

How do I know what size cylinder lock to get?

Selecting the correct size cylinder lock is crucial, whether you’re replacing an existing lock or getting a brand new one. So, if you are wondering “How do I know what size cylinder lock I need?”, here are some pointers to help you make the right choice.

If you are replacing an existing lock:

  • Measure the old lock – If you’re replacing an old cylinder lock, start by measuring the length of the existing lock. This ensures the new lock will fit perfectly;
  • Check the type – Identify the type of cylinder lock you’re replacing, whether it’s a euro, oval, thumbturn, or single/double cylinder. This information is essential to match the style correctly;
  • Security needs – Consider if you want to enhance security features. Some new locks offer additional security elements that might be beneficial;
  • Cam length – If the old lock has a cam, measure its length. Ensure the new lock has a compatible cam to work with your door’s mechanism.

If you are getting a new lock:

  • Door type – Determine the type of door you’re installing the lock on, such as wood, metal, or glass. Different doors may require different lock types and sizes;
  • Security level – Assess your security requirements. High-security locks are available with advanced features that provide additional protection;
  • Type of lock – Choose between euro, oval, thumb turn, or single/double cylinder locks based on your door and security preferences;
  • Professional adviceConsult with a locksmith or security expert for guidance. They can recommend the most suitable lock based on your specific needs;
  • Brand and quality – Research reputable lock brands and opt for high-quality locks to ensure long-lasting security and performance.

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  • Properly measuring cylinder locks is essential when replacing or upgrading locks to ensure a correct fit;
  • Cylinder locks come in various sizes, typically measured in millimetres (mm), to accommodate different door and frame types;
  • Full-size Euro cylinder locks generally range from 60mm to 120mm, with the cam centred in the barrel. Half-Euro cylinders are typically 40mm to 50mm;
  • Selecting the right size cylinder lock involves measuring the old lock or considering door type, security needs, cam length, and seeking professional advice;
  • Reputable brands and high-quality locks are recommended for long-lasting security and performance.
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