How To Measure A Mortise Lock？

Has your old mortise lock given up the ghost? Or maybe you're upgrading your door hardware for a fresh new look? Either way, you'll need to find a replacement that fits perfectly. Unlike simpler cylindrical locks, a mortise lock requires a specific pocket (the mortise) cut into the edge of the door. This means getting your measurements right is crucial for a smooth installation.

Getting the wrong size can lead to frustrating installation issues, a door that doesn't close properly, or even a security risk. Taking a few precise measurements can save you time, money, and a major headache down the road.

This guide will walk you through everything you need to know about how to measure a mortise lock. We’ll cover the essential tools, define the key terminology, and provide a clear, step-by-step process to ensure you get the perfect fit the first time.

Before You Begin: Tools & Terminology

To measure your mortise lock accurately, you won't need anything too specialized. Just grab a few common household items:

· Tape Measure: A standard retractable tape measure is perfect for this task. Ensure it has clear markings for both inches and millimeters, as some lock specifications use metric units.

· Screwdriver: You will need this to remove the existing lock from the door.

· Pen and Paper: To jot down your measurements as you go. Don't rely on memory!

Now, let's get familiar with the specific parts of the lock you'll be measuring. Understanding these terms will make the process much clearer.

· Backset: The distance from the edge of the door to the center of the keyhole or handle spindle. This is one of the most critical measurements.

· Case Depth: The total depth of the lock body that is inserted into the door.

· Case Height: The top-to-bottom measurement of the lock body.

· PZ Centers: The distance from the center of the handle spindle to the center of the round part of the keyhole. This is vital for ensuring your handle and keyhole align correctly.

· Forend/Faceplate: The metal plate on the edge of the door that the lock bolts pass through. You'll need to measure its length and width.

Step-by-Step Guide to Measuring Your Mortise Lock

With your tools ready and terminology understood, it's time to get measuring. Follow these four simple steps for accurate results. It's best to take these measurements with the old lock removed from the door so you can access all parts of the lock case.

Step 1: Remove the Existing Mortise Lock

First, you'll need to carefully remove the current lock from your door.

1.Unscrew the Handles: Start by removing the door handles. There are usually small set screws on the side or bottom of the handle levers or knobs. Loosen these to slide the handles off the spindle.

2.Remove the Faceplate Screws: On the edge of the door, you'll see screws holding the forend (faceplate) in place. Unscrew these.

3.Take out the Lock Body: Gently slide the entire lock case out from the mortise pocket in the door. It might be a snug fit, so you may need to wiggle it slightly.

Step 2: Measure the Backset and PZ Centers

These two measurements are crucial for ensuring your new handles and lock cylinder will fit properly.

· To Measure the Backset: Lay the lock on a flat surface. Measure from the front edge of the faceplate to the exact center of the handle spindle (the square hole). Common backset sizes are 2 ½ inches (63.5mm) and 2 ¾ inches (70mm), but residential locks can vary.

· To Measure the PZ Centers: Now, measure the distance from the center of the handle spindle down to the center of the circular part of the keyhole. This measurement is often referred to simply as "centers." A common center measurement for modern locks is 3 ⅝ inches (92mm).

Step 3: Measure the Lock Case

Next, measure the main body of the lock, also known as the lock case.

· Case Depth: Measure from the front of the faceplate to the very back of the lock case. Your new lock must have a case depth that is equal to or less than the depth of the mortise pocket in your door.

· Case Height: Measure the height of the case from the top edge to the bottom edge.

Step 4: Measure the Forend (Faceplate)

Finally, measure the metal plate that will be visible on the edge of your door.

· Forend Length: Measure the full length of the faceplate from top to bottom.

· Forend Width: Measure the width of the faceplate from side to side.

Double-check all your measurements and write them down clearly. Taking a photo of the lock with the tape measure in place can also be a helpful reference when you go to purchase your replacement.

Find Your Perfect Replacement

Measuring a mortise lock might seem complicated at first, but by following these steps methodically, you can be confident in your ability to find a replacement that fits seamlessly. Taking the time to get these dimensions right will prevent the frustration of a poorly fitting lock and ensure your door is both functional and secure.

Once you have your measurements, you are ready to shop for a new mortise lock. Compare your dimensions with the product specifications of potential replacements. If you are ever in doubt, don't hesitate to consult with a hardware professional or locksmith who can help you verify your measurements and select the right product for your needs.