How to Measure a Door Latch

Are you wondering which size door latch you need for your installation? You’ve come to the right place! Buying and fitting door furniture can be a bit tricky, especially if you have little to no experience. Whether you’re looking to refresh your memory or learn the tricks of the trade, we’ve got the guide to help you determine which size door latches are required.


On most internal doors at home, you will find a tubular mortice latch. This enables you to operate the door handles freely, with the latch simply holding the door shut when engaged.


Firstly, you need to know the measurements. This includes the backset size and the overall case size. The backset is the distance from the edge of the door to the centre of the door handle or door knob spindle hole. There are two common backset sizes that fitters use for residential properties, these are 57mm and 45mm.


When browsing at door latches on our website, you will notice that the mortice latch includes an additional measurement to note, this is the overall case length. These are 76mm (3 Inch) and 63mm (2 ½ Inch).



We sell these two sizes of mortice door latch in several finishes. The dimensions are detailed within the descriptions along with a diagram including the measurements.


Which Size Door Latch for New Doors?


If you’re fitting a new door, measure the distance from the edge of the door to where you wish the spindle to pass through the door, usually you’ll want this to be as close to the centre of the stile (edge panel of the door) as one of the two backset sizes will allow. The spindle is the piece of hardware that passes through the door latch to attach the handles at either side of the door.


3 Inch cases (57mm backset) are usually the preferred choice for new doors. The reason being is that this will position the handle closer to the centre of the stile and slightly further away from the door frame than the 2 ½ Inch door latch.


If fitting mortice door knobs to a new door, the recommended door latch size is also 3 Inch (57mm backset). These dimensions are preferred because it positions the knob further away from the frame, thus preventing hands from getting caught or scraping between the frame and door knob.


Which Size Door Latch for Existing Doors?


Interior doors with existing fittings will require the same door latch dimensions to the one that is currently in place to prevent filling or plunge routing.


To determine the backset and overall case length, simply remove the existing door latch and take the measurements of it. If you prefer not to remove it then you can take a ruler and measure from the edge of the door to the centre of the spindle hole (centre of the door handle or door knob).


If you’re unsure or need a little assistance, then contact us, we’d love to chat. Our award-winning Customer Service team have great expertise and will be more than happy to help.


We hope to inspire your home improvement projects and offer a variety of high-quality products that excel in both aesthetic and performance. If you love all things interior and want more home inspiration, check out our previous blogs.