How to Measure a Euro Cylinder

A euro cylinder is the barrel-shaped locking insert that sits inside the lock case of a uPVC, composite, or aluminium door. It is held in place by a single central screw and operates the multipoint locking mechanism when you turn your key. Because it is designed to be removable and replaceable, it is also the component most targeted by a technique known as lock snapping. A burglar uses a simple lever — sometimes nothing more elaborate than a pair of adjusted pliers — to snap the cylinder at its weakest point and then manipulate the cam that opens the lock. The whole process can take under a minute on a vulnerable cylinder, which is why insurers and police crime-prevention officers across London increasingly recommend anti-snap, TS007 3-star rated cylinders as a minimum standard.

The size of the cylinder determines everything: whether it fits your door, whether it operates the lock smoothly, and critically, whether it sticks out beyond the door furniture. A cylinder that protrudes more than a few millimetres past the escutcheon plate gives an attacker the leverage they need to snap it. Getting the measurement right before you buy is not a minor detail — it is the foundation of the whole job.

You will need a flat-head screwdriver and a steel rule or measuring tape. Start by opening the door so you can work comfortably. Locate the single screw in the centre of the door edge — this holds the cylinder in place. You do not need to remove the cylinder to measure it; you just need to measure the existing one or the door preparation if you are fitting fresh. With the door open, look at the cylinder from the face of the door. The measurement is always given as two figures separated by a multiplication sign, for example 35x45 or 40x40. The first figure is the internal measurement — from the centre of the fixing hole to the inside (thumb-turn) end. The second figure is the external measurement — from the centre of the fixing hole to the outside (key) end. Add them together and you have the total length, in this example 80 mm.

To measure accurately, place your rule flat across the face of the door. Find the centre of the fixing screw hole — this is your zero point. Measure from that centre point to the edge of the cylinder on the inside of the door (towards the hallway). Write that figure down. Then measure from the same centre point to the outside edge of the cylinder (towards the street). Write that figure down too. Those two numbers, in that order — internal first, external second — are your euro cylinder size. If you are replacing a cylinder on a standard 44 mm uPVC door panel, common sizes are 35x45 mm or 40x40 mm, but always measure your specific door rather than guessing from a common size, because door panels vary and even a 5 mm error means the cylinder will not seat correctly or will protrude dangerously.

Here is the detail that most people are not told when they fit a replacement cylinder themselves: if the external end of the cylinder sticks out beyond the outer face of the door furniture (the escutcheon or handle plate), it creates a snapping point that a burglar can exploit almost silently. The cylinder is engineered to break at a sacrificial groove near its centre when enough lateral force is applied — that design is a manufacturing reality, and it is why anti-snap cylinders include a secondary locking mechanism behind that groove. But even the best anti-snap cylinder offers reduced protection if it is fitted too long and protrudes significantly, because excessive overhang gives the attacker better mechanical advantage.

Across Forest Gate, Stratford, and the surrounding E7 and E15 postcode districts, uPVC doors are extremely common on both houses and flats. Many of them still carry the original cylinders fitted by builders a decade or more ago — standard cylinders with no anti-snap features and, in some cases, cylinders that were fitted slightly too long and have slowly worked their way further out as the door has settled. If your key-side cylinder protrudes more than about 3 mm past the outer handle plate, that is worth addressing. A TS007 3-star anti-snap cylinder, correctly sized so the external end sits flush or just barely proud of the furniture, is the standard our team fits as a matter of course when carrying out a door lock replacement London homeowners can trust. If you are unsure whether your current cylinder is a snapping risk, call us on 020 3757 6136 — we are available 24 hours a day, and a quick check costs nothing.

Once you have your measurement, choose a cylinder rated to TS007 3-star or at minimum to the Sold Secure Diamond standard if you want meaningful burglary resistance. These cylinders incorporate anti-snap, anti-pick, and anti-drill features, and many home insurers now factor their presence into policy terms. When you purchase, buy the exact size you measured — not the nearest available size. If the shop only has a 35x45 and you measured 35x40, the external end will sit 5 mm too far out and you are back to the snapping risk. It is worth ordering the correct size even if it takes an extra day.

If you are also thinking about how to change a lock on a timber door — perhaps a Yale-type nightlatch on a Victorian terrace — the process is different. Nightlatches use a rim cylinder that is measured differently (by diameter and body length), and older timber doors may also carry a 5-lever mortice deadlock which has no cylinder at all; that lock is changed as a complete unit. For a multipoint uPVC door, though, the euro cylinder is the only component you replace during a standard door lock change. If you find yourself uncertain partway through, or if the cylinder is damaged and will not turn, do not force it — a skilled locksmith can remove a damaged or snapped cylinder non-destructively and fit a correctly sized replacement without damage to the door.

Measuring and replacing a euro cylinder is a task most competent DIYers can manage on a door that is already open and functioning. The situation changes quickly when the cylinder is damaged, the door is locked with no working key, or the multipoint mechanism has seized. In those circumstances, forcing the job risks damaging the door leaf, the lock case, or the frame — repairs that cost considerably more than a straightforward cylinder change. As an emergency locksmith London homeowners and tenants in Forest Gate call when things go wrong, we see the results of well-intentioned DIY gone wrong on a regular basis: snapped keys in cylinders, broken spindles, door frames pulled out of alignment.

If you are locked out, the right first steps are always to check for a spare key with a trusted neighbour or family member, try other entry points you have legitimate access to, and if you are a tenant, contact your letting agent or managing agent who may hold a spare. If none of those options are available, call a professional rather than attempting to force entry yourself. As a 24 hour locksmith London team, we send a locksmith straight away and are usually with you in about 30 minutes — and we will confirm an exact price on the phone before anyone sets off, so there are no surprises on the doorstep. The final quote reflects factors including the type of lock and door, the parts needed, the time of day, and travel to your location. Call us on 020 3757 6136 any time — evenings, weekends, and bank holidays included.

Our mobile team covers Forest Gate (E7), Stratford (E15), Manor Park (E12), Upton Park (E13), West Ham (E15), Plaistow (E13), Leyton (E10), Walthamstow (E17), Hackney (E8), Bethnal Green (E2), Bow (E3), Mile End (E1W), Stepney (E1), Whitechapel (E1), Poplar (E14), Canary Wharf (E14), Canning Town (E16), Newham (E6), Ilford (IG1), Barking (IG11), Romford (RM1), Dagenham (RM10), Wanstead (E11), Leytonstone (E11), and surrounding areas of East London and the wider locksmith London service area. Every job is carried out by an experienced, insured professional.

Our services include: euro cylinder replacement, anti-snap cylinder upgrade, uPVC door lock repair London, multipoint lock repair and replacement, Yale nightlatch replacement, 5-lever mortice deadlock fitting, emergency door opening (non-destructive where possible), locked out London response, 24 hour locksmith London call-outs, emergency locksmith London for domestic and residential properties, door lock replacement London, lock change London for uPVC and composite doors, timber door lock changes, communal door lock repair, flat front door lock replacement, landlord lock change between tenancies, letting agent emergency call-out, door handle and spindle replacement, door alignment and adjustment following forced entry, security survey and advice, anti-drill and anti-pick cylinder upgrades, BS3621 mortice deadlock fitting, TS007 3-star cylinder supply and fit, door furniture replacement, and frame repair referral following break-in.

Forest Gate sits between the Wanstead Flats and the Stratford development zone, and the housing stock reflects that mix — long streets of late-Victorian and Edwardian terraces with original timber frames sit alongside 1960s and 1970s council-built blocks of flats and newer uPVC-fronted conversions. Many of the terraces on streets like Claremont Road and Capel Road have front doors that have been replaced with uPVC composite units over the years, often retaining older cylinders that were never upgraded. It is a neighbourhood where knowing the difference between a 35x45 and a 40x40 cylinder, and understanding why the size matters, is genuinely useful — not just an abstract security concern.