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How do you measure a backset on a mortise lock?

6 min read

Asked by: Nikki Rodriguez

Backset is measured from the centre of the keyhole to the edge of the lock. Most backsets are commonly measured at either 44mm (for a 64mm (2½”) lock) and 56mm (for a 76mm (3”) lock). Typically a lock adjacent to a glass panel will be 2½” (44mm) and otherwise 3” (56mm), but you should always measure to be sure.

What is the backset on a mortise lock?

The backset is the distance from the edge of the door to the center of the 2-1/8-inch bore hole.

How do I know my backset size?

Backset: A backset is the distance from the center of the cross bore, to the edge of the door. To determine the correct backset measurement for your door, you need to measure the distance from the edge of the door to the center of your cross bore.

How do you measure for a replacement mortice lock?

For a Mortice Deadlock you should only require the measurements of the Backset or the Case. This is the measurement from the front plate to the back of the lock case or the back of the slot the lock fits into in the door. If you have the old lock this measurement can be easily taken with a ruler or tape measure.

How is latch backset measured?

Overall Latch Size = Backset



An easy way to choose which latch you need is to measure from the edge of your door to the centre of your door Stile. Choose the Backset which is closest to this measurement, and the handle will be as central as possible to the Stile on your door.

What is backset size on a lock?

The backset is the horizontal distance from the edge of a door to the centre of a lockset; thus, the distance a lockset is ‘set back’ from the edge of a door is called its backset. It’s usually 1 inches or 2 inches (or 44mm and 57mm).

What backset should I use?

To determine the correct backset measurement for your door, you will need to measure the distance from edge of the door to the center of your bore hole. Two common backset measurements are 2 ¾ inches and 2 3/8 inches.

What is the most common backset door?

2 3/8″

Standard backsets are either a 2 3/8″ backset, or 2 3/4″ backset. The most common backset is 2 3/8″ but 2 3/4″ is also quite common – usually used on exterior doors. Sometimes it’s easier to measure from the edge of the door to the highest point on the bore hole.

How do you measure a lock?

Measure from the outside edge of the door (including furniture) to the centre of your door. This is dimension A and is called the External Size to Centre. Next, measure from the inside edge of your door (including furniture) to the centre of your door to find dimension B, the Internal Size to Centre.

How do you measure a door lock mechanism?

The critical dimensions are:

  1. The PZ, which is measured from the centre of the spindle (follower) hole to the centre of the top diameter of the lock cylinder (barrel) hole. …
  2. The Backset dimension, measured from the front of the lock face plate to the centre of the spindle (follower) hole.


What does 45mm backset mean?

The backset is the distance from the edge of the door to the spindle mechanism on the latch. Usually a 63mm case measurement will have a 44mm backset and a 76mm case measurement will have a 65mm backset. The backset you choose is where your door knobs will sit on the door (where the spindle goes through).

Are door locks standard size?

Standard Door Measurements



Most of the current locks require the standard 2-1/8” bore. If one wants to replace their locks on doors that have smaller diameter holes there are 2 options.

How do you measure a backset hinge?

Hinge Backset



The distance from the edge of the applied hinge leaf to the door face nearest the frame stop. This is a critical measurement and must be accurate within 1/32′′. The most common dimension is 1/4′′.

What is an adjustable backset?

Adjusting the backset ensures the deadbolt locks completely once you install it in the door. Measure the distance from the edge of the door to the center of the hole with a tape measure. The backset on a dead bolt lock only has two positions. The measurement is either 2 3/8 inches or 2 3/4 inches.

How can you tell a 5 lever mortice lock?

You can often identify a five lever mortice deadlock by the following:

  1. The words ‘5 Lever’ engraved on the internal faceplate of the lock.
  2. Mostly found on wooden doors. …
  3. Locks and unlocks from the inside and outside with a key.
  4. The lock sits within the frame of the door.


How do you open a mortise lock without a key?

That's all we're going to use just a piece of pipe. It's very very easy to throw the ball back on that door and unlock it. You watch the board. I'll just hold a lot. The board's back in there now.

What is the difference between a mortice lock and a deadlock?

The difference between a mortice deadlock and sash lock is that a mortice sashlock has a latch and bolt to open and close the lock. Where-as a mortice deadlock does not have a latch to open the lock.

How do I know if my door lock conforms to BS3621?

One way to check your front or back door locks are conforming to BS3621 is to look for the British Standard Kitemark (BSI) on the faceplate of the lock. The faceplate of the lock is viewable when you open the door; you should also see the specific standard number e.g. BS3621 stamped on the plate.

Are Euro locks BS3621?

The Fortress Euro Cylinder British Standard (BS) Deadbolt Mortice Door Lock is a high security deadlock, conforming to the BS 3621:2007; meets the exacting demands of insurance companies and the Police.

Are Chubb locks BS3621?

Chubb locks are one of the most popular BS3621 approved deadlocks for front doors in the UK, a great secure popular 5 lever deadlock.

What is en1303?

BS EN 1303:2015 is the European Standard which establishes assessment and test criteria for a cylinder to quantify its resistance to physical attack, durability and key security. BS EN 1303:2015 classifies cylinders for locks using an 8 digit coding system.

Is TS007 equivalent to BS3621?

Introducing TS 007.



Designed as a simple way to highlight enhanced product solutions to protect home-owners from opportunist burglar attack, this standard provides a level of security for replacement cylinders that is equivalent to the levels currently specified in PAS 24 and BS3621.

What is en12209?

BS EN 12209 classifies mechanically operated locks, latches and locking plates using an 11 digit coding system. This has proved necessary in order to provide a proper assessment of all the varied features of products for specific markets within Europe.