How to Measure a Euro Cylinder for Your uPVC Door (with Pictures)

Why Getting the Right Measurement Matters

If you need to replace the euro cylinder on your uPVC door — whether it has been snapped, is getting stiff, or you simply want to upgrade to an anti-snap model — the first thing you need is the correct size. Buy the wrong cylinder and it either will not fit, will stick out dangerously from the door (making it easier to snap), or will sit too far recessed for the key to turn properly.

Buying a cylinder before confirming both dimensions can leave it projecting too far, sitting too deeply or not fitting the door. This guide explains how to measure yours step by step. If you would rather have me assess and supply it, call 024 7522 4730 so the installed cylinder, surrounding furniture and current compatible-product availability can be checked.

What You Will Need

Step-by-Step: How to Remove and Measure Your Euro Cylinder

Step 1: Locate the Fixing Screw

Open your uPVC door and look at the edge (the narrow strip that faces into the frame when closed). You will see a long metal faceplate with various bolts and latches. Find the single screw that sits roughly in line with the keyhole — this is the cylinder fixing screw. It is usually a longer screw than the faceplate screws around it.

Step 2: Remove the Fixing Screw

Unscrew the fixing screw completely and set it aside. Do not lose it — you will need it to secure the new cylinder.

Step 3: Remove the Cylinder

This is where people sometimes get stuck. The cylinder will not just pull out — you need to turn the key slightly (about 10 to 20 degrees) so that the cam (the small metal tongue on the back of the cylinder) aligns with the slot in the mechanism. With the key turned slightly, you can then pull or push the cylinder out from either side of the door.

If the cylinder is really stuck, try wiggling the key gently while applying steady pressure. Do not force it — if it will not budge, the cam may not be aligned correctly. Keep adjusting the key angle until it slides out.

Step 4: Measure From the Screw Hole to the Outside End

Lay the cylinder on a flat surface. You will see the screw hole in the middle section of the cylinder. Measure from the centre of this screw hole to the end that faces outside your door. Note this measurement in millimetres.

Step 5: Measure From the Screw Hole to the Inside End

Now measure from the centre of the screw hole to the other end — the side that faces inside your home. Note this measurement separately.

Step 6: Determine the Cylinder Size

Your cylinder size is expressed as two numbers: outside measurement / inside measurement. For example, if the outside measures 35mm and the inside measures 35mm, you have a 35/35 cylinder (70mm overall). If the outside is 40mm and the inside is 45mm, you have a 40/45 cylinder.

Step 7: Note the Cylinder Type

Check whether your cylinder is:

Common Euro Cylinder Sizes for Coventry Doors

Euro cylinders come in many symmetric and offset sizes. Examples you may encounter include:

The cylinder should be correctly sized for the door and protective furniture. Noticeable external protrusion is a reason to have the fitted system assessed because it can expose more of the cylinder to attack. Read the guide to lock snapping for the evidence and certified protection options.

What Happens If You Buy the Wrong Size

Too Long

If the cylinder is too long, it will protrude from the door face. On the outside, this creates a snapping risk — a burglar can grip the protruding cylinder with pliers or a wrench and snap it. On the inside, it just looks wrong and may foul against the thumbturn or handle.

Too Short

If the cylinder is too short, it will sit recessed inside the door. The key may not reach properly, or the cam may not engage with the mechanism correctly. In some cases, the key will turn but the lock will not actually operate — extremely frustrating if you have just fitted a brand new cylinder.

Wrong Type (Key/Key vs Key/Thumbturn)

This is not the end of the world — the cylinder will still fit — but a thumbturn where you expected a key (or vice versa) is inconvenient and may not match your needs. If you are upgrading, I generally recommend key/thumbturn for most residential doors as it allows quicker exit in an emergency.

Where to Buy the Right Cylinder

You have several options:

A Word on Security When Measuring

If you are measuring because you want a security upgrade, check independent certification as well as size. Police.uk's door and window lock advice recommends a 3-star TS007 cylinder when a euro cylinder is changed. DHF's TS007 guidance also explains the tested 1-star cylinder plus 2-star furniture combination. These standards address recognised attacks, but no product eliminates every risk.

For a practical comparison of selection criteria, see the euro cylinder upgrade guide.

Should You Measure Yourself or Call a Locksmith?

If you are comfortable with a screwdriver and a tape measure, the steps above provide a starting point for measuring your cylinder. Selecting a replacement also requires the exact dimensions, cam, surrounding furniture and current certification to be checked rather than relying on a brand or label alone.

If you would rather have the door assessed, call 024 7522 4730 with the full postcode to confirm the exact address, current availability and ETA for a location listed on the areas page. Anti-snap cylinder fitting starts from £59; the exact quote depends on the size, certified product, furniture, and work required. See current prices and the lock upgrade service.

For more on uPVC door locks and maintenance, see our uPVC door maintenance guide and our uPVC lock repair service page.