How to Choose the Right Size Garage Door Lock for Your Door

Garage doors are one of the largest entry points to a home, and the lock that secures them plays a crucial role in keeping the property safe. A lock that is the wrong size will not fit properly, will be awkward to use, and may even compromise security. Unfortunately, many homeowners in the UK underestimate the importance of choosing the correct size lock for their garage door. They assume one size fits all, only to discover that the lock they bought does not align with the existing holes, that the spindle is too short, or that the cylinder sticks out too far and is vulnerable to snapping.

This guide explains how to choose the right size garage door lock for your door. We will look at the different types of garage locks, the measurements you need to take, common mistakes to avoid, and practical examples to help you make the right choice first time.

Why size matters when choosing a garage lock

A garage lock is not a decorative accessory. It is a precision part of a system that includes the handle, rods, and door panel. Choosing the wrong size affects both security and usability.

  • A lock that is too small may not reach through the thickness of the door.
  • A cylinder that is too long will protrude, making it easier for intruders to snap.
  • Fixing bolts that do not align with existing holes will require drilling, which can weaken the door.
  • Handles that are not matched to the lock size may wobble or fail prematurely.

Correct sizing ensures the lock fits seamlessly, engages the mechanism fully, and provides the intended level of protection.

Types of garage door locks

Different garage door designs require different locks, and the measurements you need to take vary depending on the type.

T-handle locks

T-handle locks are commonly used on up-and-over garage doors. The external handle is shaped like a T, and a spindle passes through the door to connect with rods inside. Key measurements include the fixing centres (the distance between the bolts) and the spindle length.

Euro cylinder locks

Euro cylinders are widely used on sectional and modern up-and-over doors. They are also common on side doors to garages. The critical measurement here is the cylinder length, which must match the thickness of the door and handle assembly.

Mortice locks

Mortice locks are used on side-hinged garage doors, similar to house doors. The key measurements are case depth, backset, and forend length. Choosing the wrong size means the lock will not fit into the mortice cavity.

Slide locks

Slide locks are internal bolts used on roller doors. Size is determined by the bolt length and how far it needs to slide into the track.

Padlocks with hasps

Some garages use padlocks and hasps for secondary security. In this case, size refers to the shackle thickness and clearance needed to fit the hasp securely.

How to measure for the right size lock

Measuring for T-handle locks

  1. Measure the distance between the fixing bolts that pass through the door. Common sizes are 50 mm, 60 mm, or 75 mm.
  2. Measure the spindle length from the back of the handle to the internal mechanism. It must be long enough to reach but not so long that it protrudes excessively.
  3. Measure the overall diameter of the handle base to ensure it covers the existing hole neatly.

Measuring for euro cylinders

  1. Locate the centre fixing screw that holds the cylinder in place.
  2. Measure from the screw to each end of the cylinder. For example, a 30/40 cylinder measures 30 mm on one side and 40 mm on the other.
  3. Ensure the cylinder sits flush with the handle once installed. If it sticks out, it is vulnerable to snapping.

Measuring for mortice locks

  1. Measure the case depth (the distance from the front of the forend to the back of the lock case).
  2. Measure the backset (the distance from the edge of the door to the centre of the keyhole).
  3. Measure the forend length and width to ensure the new lock covers the cavity neatly.

Measuring for slide locks

  1. Measure the length of the bolt. It must extend far enough into the track to secure the roller curtain.
  2. Check the height and width of the slide mechanism to ensure it fits within the available space.

Measuring for padlocks

  1. Measure the diameter of the shackle. It must fit through the staple of the hasp.
  2. Measure the vertical clearance of the shackle to ensure it can close over the hasp securely.

Common mistakes when choosing garage lock sizes

Assuming all locks are the same

T-handles, cylinders, and mortice locks all come in different sizes. Choosing without measuring is one of the most common mistakes.

Forgetting about door thickness

If the spindle or cylinder is too short, it will not reach through the door. If it is too long, it will stick out and reduce security.

Ignoring fixing centres

Fixing bolts must align with existing holes. If they do not, drilling new ones can weaken the door panel.

Overlooking handle compatibility

On many garage doors, the handle and lock are part of the same system. Replacing only one without checking compatibility can cause wobbling or poor engagement.

Not considering insurance requirements

Insurers may require locks that meet British Standards. Choosing a lock purely by size without checking compliance can affect cover.

When to replace like-for-like and when to upgrade

If your existing lock fits well, works smoothly, and meets security standards, replacing like-for-like is usually the simplest option.

However, replacement is also an opportunity to upgrade. If you currently have:

  • A basic T-handle, consider a reinforced version with a hardened barrel.
  • A standard euro cylinder, upgrade to an anti-snap, anti-drill model.
  • A corroded mortice lock, replace it with a British Standard 5-lever version.

Upgrading ensures your new lock not only fits but also offers better protection.

Tools needed for fitting a new lock

  • Screwdrivers (flathead and Phillips).
  • Tape measure for accurate sizing.
  • Drill and bits if new holes are required.
  • Spanner or socket set for handles.
  • Lubricant such as silicone spray or graphite powder.

Practical examples from UK homeowners

A homeowner in Manchester replaced a euro cylinder on a sectional door without measuring. The new cylinder stuck out by 10 mm, making it vulnerable to snapping. They later replaced it with a correctly sized anti-snap model that sat flush.

In Leeds, a family tried to replace an old T-handle lock with a new one but forgot to check the fixing centres. The new lock did not align with the existing holes, leaving them with a weakened panel after drilling. They eventually ordered a 75 mm fixing centre lock that fitted perfectly.

In Brighton, a property near the coast suffered repeated corrosion problems. The homeowner upgraded to a marine-grade stainless steel mortice lock on their side-hinged garage door. Careful measurement of case depth and backset ensured a perfect fit, and the new lock has resisted rust for years.

Maintenance to keep locks working smoothly

Even the right size lock will not perform well without maintenance.

  • Clean the lock exterior monthly to remove dirt and grit.
  • Lubricate the keyway twice a year with graphite powder or silicone spray.
  • Check fixings annually to ensure bolts and screws remain tight.
  • Inspect for rust or corrosion, particularly after wet or cold weather.

Final thoughts

Choosing the right size garage door lock is not just about convenience, it is about security. A correctly sized lock fits seamlessly, works smoothly, and provides the protection your garage and home deserve. The process involves measuring carefully, avoiding common mistakes, and considering whether an upgrade is worthwhile at the time of replacement.

For UK homeowners, the key is not to assume one size fits all. By taking the time to measure fixing centres, spindle lengths, cylinder sizes, and mortice dimensions, you ensure the lock you buy will fit perfectly and last for years. When combined with regular maintenance and sensible upgrades, the right size lock becomes a reliable line of defence for your property.

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