How to Measure Your Door For Locks

Accurately measuring your door for a lock depends completely on what kind of lock you'll be using. The two most prominent types of lock are deadlocks and sashlocks, so we'll concentrate on these two for now. The process for measuring a door for any other type of lock will probably be a variation on the process used for these main two.

Measuring your Door for a Mortice Deadlock

A simple deadlock (deadbolt) is an effective and easy way to boost the security of your house. Most burglars make entry through door and windows, and the visible presence of a deadbolt can often be enough to make an opportunistic thief reconsider targeting you. Installing deadlocks can also save you cash on your home insurance; get in touch with your insurer to see if you can benefit.

If you've already purchased your deadlock and you're measuring your door to fit it, then the process is a little easier, and we'll discuss this first. If you haven't yet bought your deadlock and you're measuring your door to find which size is best for you, it's a bit more complicated, and we'll come back to it in a moment.

First, if you've already bought your deadlock, then open the packaging in which it came. You'll find a template - it's usually made of paper or card - which you can use to mark out where you want your bolt to go, and make the correct measurements accordingly. With the template close by, and a tape measure and pencil in hand, first judge whether you want your deadbolt above or below your current door hardware. It's most common to position the deadlock lower on the door, but there's no real reason for this and the bolt can safely be positioned anywhere you want.

Positioning the Deadlock


There is one convention worth bearing in mind though, and it's this: place your deadlock at least twelve inches away from the existing door hardware, whether you choose to install the bolt above or below it. This is because it's best to spread the strength provided by locking mechanisms down the length of the door, rather than concentrating it neatly in one area.

Once you've settled on a position for the deadbolt, tape the template in place, ensuring that it's square and level with the door, and use your pencil to mark where the drill holes will go. Then repeat the process on the other side of the door. Simple. Your door is now measured and ready to fit the deadbolt.

However, if you haven't yet bought your deadbolt, you probably won't have a template to use. Therefore, to measure your door you need to improvise the measurements. First, measure the backset of your current door hardware. 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). Then, after settling on the location you'd like for your deadlock, measure the backset from the edge of the door in that location and mark it with your pencil. Repeat the process on the other side of the door. Now check whether your door will accept either the smaller or larger case lock, 67mm or 80mm, without interfering with any recessed panels, glass or embedded decoration.

Measuring your Door for a Mortice Sashlock


Since a mortice sashlock is a little more complicated - but very similar to a deadlock - the measurements you need are not so different. The first measurement is the 'stile' of the door. The stile is the horizontal distance from the edge of the door to the edge of any paneling or glass your door might have. If your door's surface is completely flat, without any panels, glass or embedded decoration, then you don't need to measure this. If your door does have panels, glass or embedded decoration, then you need to measure the distance between the edge of the door and the beginning of them. Obviously the stile measurement varies between door designs, but it's usually around 90mm to 125mm.

You don't need to worry whether your door is left- or right-handed. The majority of locks are reversible.

The stile will decide which size of lock you can use. Determine whether you can fit a 67mm deep or an 80mm deep lock without interfering with any of the door features. Once you have determined this, look at which backset will best suit your door, either the smaller 44/45mm or larger 57/60mm backset. Now consider how wide the backplate of your lever handle set is or the diameter of the rose your lever is on and make sure the position of the handle set on the door is acceptable. Check particularly that the backplate or rose will not interfere with any panelling, door frames or, if the doors are double and rebated, that the handle plates don't cover any of the rebate.

If your door has been pre-drilled for a mortice lock, then you will need to measure the backset, which in this case would be the distance from the edge of the door to the centre of the pre-drilled hole. If there are two holes drilled, one above the other, you'll need to know their distance from one another.

Most other types of locks will require similar - if not identical - measurements. If the lock you need to measure your door for is mounted to the surface, then follow the procedure outlined above. We hope this information helps you choose the right lock for you; if you have any further questions please contact us via the details on our Contact Us page or browse our resources for the information you need.?