How to measure for a door cylinder lock

You need only two simple measurements

Written by Lucy Thornton ,
Published on December 18, 2023 at 1:38:30 PM PST December 18, 2023 at 1:38:30 PM PSTth, December 18, 2023 at 1:38:30 PM PST
How do I know what size cylinder I need?

You can replace your door cylinder fairly easily with some basic DIY skills and tools.

Coastal Group's friendly Sales and Support Advisor Joe Hunt has put together a quick guide showing how to measure for a new door cylinder.

You just need a couple of key measurements to get started, which together give you the overall length of your cylinder.

Step 1: Door thickness

Start with the attack side (or the exterior of the door); measure first from the outside to the centre of the door.

Step 1: Measure the thickness of the door

Here we have a 44mm door. We can see that the lock is centred, so that's 22mm from the outside of the door to the centre of the cylinder.

Step 2: Thickness of door hardware

We now need to know the depth of any hardware fitted to the outside of the door, for the cylinder to sit neatly against.

Step 2: Measure the thickness of any door hardware

On this door, the escutcheon is an extra 11mm thickness.

This tells us the cylinder needs to be at least 33mm on the attack side (i.e. 22mm + 11mm). All cylinders go up in increments of 5mm so with an attack side measurement of 33mm you need to round-up, making the first measurement 35mm.

Step 3: Thickness of internal door furniture

The next measurement we need is on the internal side of the door.

Take the lever handle and measure the thickness of the backplate.

Step 3: Measure the thickness of the interior handle backplate

Here it's around 14mm in depth, so we add that onto the original measurement from the centre of the door to the outside to get 36mm (22mm + 14mm).

When rounded (remember that cylinders go up in increments of 5mm) the second number is therefore 40mm.

For this door you will need a cylinder which is 35/40 (75mm in total).

If you need any help measuring for a new door cylinder, please don't hesitate to get in touch with our team here at Coastal Group.

Browse the range of cylinders and thumbturns from Coastal Group

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