How to Measure a Euro Cylinder

A euro cylinder is the barrel-shaped lock mechanism that slots into the lock case on most modern uPVC and composite front and back doors. It is the part your key actually enters. It is held in place by a single central screw through the door handle or escutcheon plate, and that simplicity is both a convenience and a security risk — if the cylinder protrudes too far, a burglar can snap it in seconds using nothing more sophisticated than a screwdriver and a sharp pull. This is known as cylinder snapping or lock snapping, and it remains one of the most reported methods of forced entry on residential streets in the London Borough of Greenwich.

The measurement matters because euro cylinders are sized by the total length of the cylinder and the position of the central fixing hole. Buy one that is even a few millimetres too long on the outside and you have created that dangerous protrusion. Buy one that is too short and the cam inside may not engage the lock mechanism correctly, leaving you with a door that will not lock at all.

You will need a flat-head screwdriver to remove the door handle or escutcheon, a tape measure or ruler, and a pen and paper. Start with the door open so you are not accidentally locked out during the process. Remove the single central fixing screw on the door handle — it usually sits in the centre of the handle or the rose plate — and slide the handle off. The cylinder will now be visible in the lock case. Do not remove the cylinder itself; you can take all the measurements you need while it is still in the door.

Euro cylinders are measured in millimetres and expressed as two numbers separated by a multiplication sign — for example, 35x45 or 40x40. The first number is the measurement from the outside face of the door to the centre of the fixing hole (the cam hole). The second number is the measurement from the centre of the fixing hole to the inside face of the door. So for a 35x45 cylinder, the total length is 80mm. To measure: place your ruler or tape at the outer edge of the cylinder (the side facing the street) and measure to the centre of the fixing hole — that is your first number. Then measure from the centre of the fixing hole to the inner edge of the cylinder — that is your second number. Write both down. If the door has a handle on each side, also note whether there is a thumb-turn on the inside (a small oval knob you can turn without a key) rather than a keyhole, as this affects the cylinder type you need to order.

Here is the scenario that plays out in burglaries across Eltham and the wider locked out London belt every week. A homeowner has a uPVC door fitted with a standard euro cylinder that sticks out 10 or 15mm beyond the door furniture. A burglar pushes a screwdriver into the gap, grips the exposed section of the cylinder with a pair of mole grips or adjustable pliers, and applies lateral force. The cylinder snaps at its weakest point — just outside the fixing hole — and the door opens in under 30 seconds. No glass broken, no noise, no forced door frame.

The fix is straightforward: measure correctly so the installed cylinder sits flush with or no more than 1mm proud of the surrounding door furniture, and choose an anti-snap cylinder. Look for products rated to TS007 3-star or at least carrying the Sold Secure Diamond rating. These cylinders have a sacrificial snap point engineered into the outer section — the outer portion breaks away if forced, but the inner mechanism remains intact and the door stays locked. If your insurer requires BS3621 compliance (many do, particularly for terraced houses and flats in SE9 and SE3), check that any replacement cylinder is compatible with your existing lock case. If you are unsure, this is exactly the kind of job where a quick call to a qualified locksmith saves you a wasted trip to the hardware shop. Call 020 3757 5833 and we can advise you over the phone, then come out to Eltham or anywhere nearby to fit the right cylinder the same day.

The most frequent mistake homeowners make is measuring only the total length of the old cylinder and ordering the same total — say 80mm — without checking how that 80mm is split across the fixing hole. A 35x45 and a 45x35 are both 80mm total, but they are not interchangeable: fitting the wrong one leaves the cylinder either protruding on the outside or sitting too deep on the inside, both of which cause problems. Always record the two numbers separately.

If a cylinder has already been snapped — either by a burglar or by a key broken off inside — do not try to open the door using improvised methods. Lock picking and bypass techniques are skilled work, and amateur attempts risk damaging the lock case, the door slab, or the multipoint locking mechanism, which can make the door impossible to close securely even after repair. If you are locked out in the Eltham area, check whether a ground-floor window has been left open, whether a neighbour has a spare key, or whether a rear entrance to the garden is accessible. If none of those options are available, we send a locksmith straight away and are usually with you in around 30 minutes. We handle door lock replacement London-wide around the clock, and as a 24 hour locksmith London we are available on evenings, weekends and bank holidays — not just during office hours.

Once you have your two measurements, you are looking for a cylinder of the correct size with the security features that suit your door. For most uPVC and composite doors on residential streets in Eltham, we recommend anti-snap cylinders rated to TS007 3-star. For timber doors with a traditional mortice deadlock, the cylinder question does not apply — these use a different mechanism — but if you are considering how to change a lock or how to change a door lock on an older timber front door, the standard is a 5-lever mortice deadlock rated to BS3621. Many insurers in the Greenwich area require this as a minimum for contents cover to remain valid.

As a fully insured mobile locksmith London team, we cover uPVC door lock repair London, emergency locksmith London call-outs, lock change London jobs, and straightforward cylinder upgrades across SE9, SE3, SE12, SE13, SE18, and beyond. Our services include: euro cylinder replacement, anti-snap cylinder fitting, TS007 3-star cylinder upgrades, multipoint lock repair, uPVC door lock repair, composite door lock replacement, door lock replacement, nightlatch replacement, 5-lever mortice deadlock fitting, BS3621 lock upgrades, snap repair and door restoration, locked-out assistance and non-destructive entry, door handle and escutcheon replacement, door alignment and adjustment, door won't close repair, lock barrel replacement, patio door lock repair, French door lock repair, back door lock change, communal entrance lock repair, landlord lock change between tenancies, tenant lockout response, letterbox replacement, door reinforcement plate fitting, and security surveys for residential properties. Whether you have measured your cylinder and simply need someone to fit the right part, or you are locked out at midnight on a Sunday, we are here.

The final price for any lock work depends on a number of factors: the type of door and lock case, the cylinder size and security rating required, the time of day (evenings, weekends and bank holidays carry different rates), the distance our locksmith travels to your address, and any additional parts or hardware needed. We never quote a vague range and then surprise you on arrival — we confirm an exact up-front price on the phone before anyone leaves for your property, so you can make an informed decision with no pressure. If you are dealing with an emergency locksmith London situation and need someone out tonight, call 020 3757 5833 and we will give you a clear figure straight away.