Views: 0 Author: Site Editor Publish Time: 10-09-2025 Origin: Site
If you're looking to replace a lock on an older door or upgrade your home's security, you've likely come across the term "mortise lock." These sturdy, reliable locks have been a staple in homes and buildings for over a century. A common question that arises during this process is: are all mortise locks the same size?
The short answer is no. Unlike more standardized modern locks, mortise locks come in a wide variety of shapes, sizes, and configurations. This can make finding a direct replacement a bit of a challenge. This guide will walk you through everything you need to know about mortise lock sizing, from how to measure them correctly to what to do when you can't find an exact match. By the end, you'll have the confidence to tackle your lock replacement project with ease.
First, let's clarify what makes a mortise lock unique. The term "mortise" refers to the pocket or recess cut into the edge of a door where the lock body is fitted. This is different from a cylindrical or tubular lock, which only requires a couple of round holes drilled through the door.
A mortise lock consists of several components:
· Lock Body: The main part of the lock that sits inside the door mortise. It contains the latch and deadbolt mechanisms.
· Lock Trim: The decorative plates, handles, knobs, or levers that are visible on the outside of the door.
· Strike Plate: The metal plate installed on the door frame that the latch and deadbolt extend into to secure the door.
· Keyed Cylinder: The part where you insert the key to lock or unlock the deadbolt.
Because the lock body is housed within the door itself, mortise locks are generally considered more robust and secure than their cylindrical counterparts. They are often found in older homes, historic buildings, and high-end commercial properties.
If you’ve ever tried to replace an old mortise lock, you’ve probably discovered that it’s not as simple as picking a new one off the shelf. There is no universal standard for mortise lock dimensions, which leads to significant variation. Several factors contribute to this diversity.
Many older mortise locks were produced before manufacturing standards became common. Different companies in different eras had their own proprietary designs and dimensions. A lock made in the 1920s by one manufacturer will almost certainly have different measurements than one made by a competitor in the 1950s.
Mortise locks are designed for various applications, each requiring a different internal mechanism and, therefore, a different size. A simple passage lock for an interior closet door will have a much smaller and simpler body than a complex entry lock with a deadbolt and multiple locking points.
The dimensions of the door itself play a crucial role in determining the size of the mortise lock. Thicker, heavier doors can accommodate larger, more substantial lock bodies. The style of the door and its trim can also influence the size and shape of the lock and its faceplate.
Since there is no standard sizing, accurately measuring your existing mortise lock is the most critical step in finding a suitable replacement. Taking precise measurements will save you time, money, and a lot of frustration. You'll need a tape measure or a ruler, and it's helpful to have a notepad to jot down the dimensions.
Here are the key measurements you need to take:
The backset is the distance from the edge of the door to the center of the keyhole or knob hub. This is arguably the most important measurement. If the backset of the new lock doesn't match the old one, the holes for the handle and key cylinder in your door won't line up. Common backset sizes for mortise locks are 2 ½ inches and 2 ¾ inches, but they can vary.
The lock case (or lock body) is the rectangular box that fits inside the door. You'll need to measure its:
· Height: The top-to-bottom measurement of the case.
· Depth: How far the case extends into the door from the edge.
· Thickness: The width of the lock case. The mortise pocket in your door is cut to this specific thickness, so a new lock must match it closely.
The faceplate is the metal plate you see on the edge of the door, through which the latch and deadbolt protrude. Measure its:
· Length: The top-to-bottom measurement of the faceplate.
· Width: The side-to-side measurement.
Also, note the shape of the faceplate's corners. Are they square or rounded? This detail is important for ensuring the new plate fits neatly into the existing recess on the door's edge.
This refers to the center-to-center distance between different components of the lock.
· Center-to-Center (C-C): The distance from the center of the knob/lever hub to the center of the round part of the keyhole. This measurement ensures your existing trim holes will align.
It’s quite possible that after searching, you won’t find a new mortise lock that is an exact one-to-one replacement for your old one. Don't worry—you still have options.
Many manufacturers offer retrofit kits designed to help you install a new mortise lock into a door that was prepared for an older, differently sized model. These kits might include adapter plates or other hardware to bridge the size difference.
If you're comfortable with some woodworking, you can modify the mortise pocket in your door to accommodate a new lock. This might involve enlarging the pocket with a chisel or router. While effective, this requires precision and the right tools. If you're not confident in your skills, it’s best to hire a professional locksmith or carpenter.
In some cases, it might be easier to abandon the mortise lock altogether and install a modern cylindrical lock. This is a more involved process, as it requires filling the old mortise pocket and drilling new holes in the door. There are special kits available to help fill the large mortise cavity and prep the door for a new lock style. This is often a last resort, especially for historic doors where preserving the original hardware style is a priority.
When in doubt, a professional locksmith is your best resource. Locksmiths, especially those who specialize in older hardware, have access to a wide range of products, including vintage and hard-to-find parts. They can identify your existing lock, source a compatible replacement, or professionally modify your door to accept a new one. Their expertise can save you a significant amount of guesswork and potential damage to your door.
While mortise locks are not all the same size, finding a replacement is far from impossible. The key is to be methodical. By taking careful and accurate measurements of your existing lock—paying close attention to the backset, case dimensions, and spacing—you significantly increase your chances of finding a compatible replacement.
If a perfect match proves elusive, remember that you have options ranging from retrofit kits to professional assistance. Armed with the right information and a clear plan, you can successfully navigate the world of mortise locks and ensure your door is both secure and stylish.
