How to Measure a Euro Cylinder

A euro cylinder — sometimes called a barrel lock or a euro profile lock — is the oval-shaped brass or steel core you see on the face of most uPVC and composite doors, as well as many timber doors fitted with a modern multipoint locking system. The cylinder is held in place by a single retaining screw through the door handle plate, and it operates every locking point up and down the edge of the door when you turn the key. Because the entire door depends on this one component, its size and specification matter enormously.

Euro cylinders are sold by their total length, expressed as two numbers that measure each side from the centre fixing hole outward — for example, 35/45, 40/40, or 35/55. If you order the wrong size, the cylinder either will not fit at all, or it will stick out beyond the door furniture and become dangerously easy to snap. Getting the right measurement before you buy or before you call a locksmith for a lock change London is the single most important step in the process.

Remove the door handle faceplate screws and gently draw the handle back so you can see the cylinder clearly. You do not need to remove the cylinder itself. Place your tape measure at the outer face of the cylinder — the keyhole side that faces the street — and measure to the centre of the retaining screw hole. Write that number down: this is your external measurement. Now measure from the centre of the retaining screw hole to the inner face of the cylinder — the thumb-turn side that faces your hallway. Write that number down too. The two figures together give you your cylinder size. Add them, and you have the total length. So if your external side is 35 mm and your internal side is 45 mm, you need a 35/45 cylinder with a total length of 80 mm.

A few practical tips: always measure the existing cylinder while it is still in the door, because the door thickness and handle position determine what will fit. Use a steel rule rather than a fabric tape if you have one, as fabric tapes can sag by a millimetre or two. If the door has a letter box near the lock, measure from both sides independently rather than trying to reach around it. If you are unsure whether your measurement is accurate, photograph the cylinder face-on with a coin for scale and send it to us — our experienced team can usually confirm the size from a clear image before we arrive.

Here is the safety point that most DIY guides gloss over: a euro cylinder that protrudes more than about three millimetres beyond the door handle escutcheon plate can be snapped off in seconds using nothing more sophisticated than a pair of mole grips and a screwdriver. Once the outer portion of the cylinder is sheared away, the internal mechanism is exposed and the door opens. This is cylinder snapping — a common method used in burglaries across South West London — and it is entirely preventable with the right cylinder size and specification.

The first line of defence is correct sizing so that no excess cylinder is exposed. The second is choosing an anti-snap cylinder rated to TS007 3-star or at least carrying the Sold Secure Diamond rating. These cylinders have a sacrificial break point engineered into the outer section: if a burglar tries to snap them, only a replaceable outer portion gives way, and the internal mechanism remains locked. Many home insurers now ask specifically whether your uPVC or composite door has an anti-snap cylinder — if yours does not, a door lock replacement London homeowners arrange proactively is far less disruptive than dealing with a break-in. If you would like us to assess your current cylinder and recommend the right upgrade, call 020 3757 5840 — we are available 24 hours a day, every day of the year.

The most common euro cylinder sizes found on Wandsworth's mix of Victorian terraces converted into flats, 1970s and 1980s semi-detached houses, and newer-build townhouses around Earlsfield and Summerstown tend to fall between 70 mm and 90 mm total length, with the external side usually being the shorter measurement. A 35/45 (80 mm total) is very common on uPVC doors. Composite doors on newer builds often take a 35/50 or 40/50. Older timber doors that have been retrofitted with a multipoint lock can vary more widely — always measure rather than guess.

Pay particular attention to whether the existing cylinder is non-standard because a previous owner had the door modified, or because the frame has been adjusted after a repair. If you find that one side measures significantly longer than the other — say a 30/60 — that is worth flagging, because it may mean the cylinder is seated incorrectly or that a non-standard handle plate has been fitted. Our engineers carry a broad range of cylinder sizes and regularly handle upvc door lock repair London calls where the original cylinder was simply the wrong size from the outset, leaving the lock stiff, the thumb-turn unresponsive, or the door impossible to deadlock from outside.

Measuring your cylinder is a sensible weekend task, but there are moments when the problem is already urgent. If your key turns stiffly or grinds, the cylinder may be misaligned, worn, or the wrong size — and a stiff cylinder has a habit of failing completely at the worst moment. If the cylinder has already been partially snapped, do not try to operate the lock further; a remaining stub can damage the cam inside the gearbox of a multipoint lock, turning a cylinder replacement into a more involved lock change. If you are locked out and the door has a uPVC multipoint lock, avoid anything you may have read about how to pick a door knob lock or how to pick a lock door knob — euro cylinders are not door-knob locks and amateur attempts to manipulate them cause damage that significantly increases the complexity of the repair.

In a lockout, the right first steps are always: check every other door and accessible window, ask a family member whether they have a spare key, and contact your letting agent or managing agent if the property is rented, as they may hold a copy. If none of those options apply, call an experienced 24 hour locksmith London team rather than attempting anything yourself. As a 24/7 mobile locksmith Wandsworth residents and landlords rely on, Earlsfield Locksmith covers the whole SW18 area and beyond — including Tooting, Balham, Battersea, and Clapham. We will confirm an exact up-front price on the phone before anyone sets off, so you know precisely what to expect. The price we quote accounts for the type of lock involved, whether parts are needed, the time of day, and how far our nearest engineer needs to travel. Call 020 3757 5840 any time — evenings, weekends, and bank holidays included.

Once you have your measurement, here is what to look for when selecting a replacement. First, match the size as closely as possible, ideally with no more than one to two millimetres of cylinder proud of the escutcheon on the external side. Second, look for the TS007 3-star mark or Sold Secure Diamond on the packaging — these are the standard assurances that the cylinder has been independently tested against snapping, drilling, and picking. Third, check whether your door is handed: most euro cylinders are universal, but a small number of multipoint locks require a specific cylinder profile, so if you are unsure, bring the old cylinder with you when you shop, or let our team handle the selection as part of a door lock replacement London visit.

[9] Finally, consider whether a change of lock or cylinder is an opportunity to improve overall security rather than simply like-for-like. If you are moving into a new flat or house, changing the cylinder means any keys held by previous tenants, estate agents, or contractors are immediately redundant. If the door has a keypad or a code-operated lock and you need to know how to change the code on a keypad door lock or how to change the door lock code on a digital model, that is an entirely separate process covered by the manufacturer's instructions — and our team can assist with those locks too. The key principle in every case is that your lock should be the right size, the right specification, and correctly fitted — because a lock that is any one of those three things wrong offers far less protection than it appears to.