Euro cylinder sizing
What size euro cylinder do I need? How to measure it properly.
Measure A and B from the centre screw. Common sizes, offsets, and the 3mm rule that keeps your door secure.
A euro cylinder is the brass lock with the keyhole that sits in the edge of almost every UK uPVC and composite door. Getting the size right matters for two reasons: a cylinder fitted too long sticks out past the handle and becomes the weak point a burglar snaps, and one fitted too short will not drive the lock properly. The good news is measuring it is a two-minute job once you know the trick, which is to measure each half from the central fixing screw rather than end to end. This guide walks you through it with a diagram, lists the common sizes, and explains the offset that catches most people out when they buy online. If you would rather I measured and fitted it, that is a small, honest job and the price is on the phone before I set off.
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What a euro cylinder is, and why size matters
The euro cylinder is the self-contained brass lock that holds the keyhole on a uPVC or composite door. It sits in the strip-edge of the door, held by a single fixing screw, and it is the part you change when keys are lost or when you want to upgrade security, because it swaps out without touching the door, the handle or the multi-point gearbox. Almost every uPVC and composite door in the country uses one.
Size matters more than people expect. A cylinder that is too long stands proud of the handle, and that exposed lip is exactly what a burglar grabs in a snap attack. The Master Locksmiths Association advises that a euro cylinder should not protrude more than 3mm from the handle, and ideally sits flush. A cylinder that is too short is the opposite problem: the cam in the middle cannot reach far enough to drive the lock, so the key will not turn properly or the bolt will not throw. The right size sits as close to flush as possible on both faces, which is why you measure the two halves, not just the overall length.
How to measure a euro cylinder, step by step
The whole trick is to measure from the centre, not from the ends. The diagram below shows it: the central fixing screw is your reference point, and you measure out to each face separately. The visible steps here match the HowTo schema embedded on this page. Total time is about eight minutes, most of which is getting the old cylinder out.
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Take the cylinder out, or measure it in place
3 min
On a uPVC door, undo the single long fixing screw on the door edge (the forend strip, just below the latch). Put the key in, turn it a few degrees to line the cam up, and the cylinder slides straight out. If you would rather not remove it, you can measure it in place from the centre screw, it is just easier to read off the bench.
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Find the centre: the fixing-screw point
1 min
Look at the underside of the cylinder for the threaded hole the fixing screw passes through. That central point is your reference for both measurements, because it is where the cam sits and where the cylinder lines up in the door. Everything is measured from there, not from one end.
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Measure side A: centre to the outside face
1 min
With a steel tape or ruler, measure from the centre of the fixing screw to the outside face of the cylinder (the side that faces the street). Write it down. It will almost always be a multiple of 5mm, commonly 30, 35, 40, 45 or 50mm.
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Measure side B: centre to the inside face
1 min
Now measure from the centre of the same screw to the inside face (the side that faces into your home). Write that down too. If one side has a thumbturn knob instead of a keyhole, note which side, because thumbturn cylinders are sized the same way but ordered as a turn cylinder.
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Add A + B, and round to the nearest 5mm without going proud
2 min
A plus B is your overall length, and the two halves are how you quote it (for example 40/50, eighty millimetres of cylinder split as 40mm outside and 50mm inside). Cylinders come in 5mm steps, so if your reading lands between sizes choose the nearest standard that keeps the cylinder as close to flush as possible. Never round up on the outside face so far that it stands proud of the handle, because a protruding cylinder is the snap-attack weak point.
Work out your size: the calculator
Measured your two halves from the centre fixing screw? Put them in below and I will tell you the size to order, whether it is symmetric or offset, and whether it will sit flush. It runs entirely in your browser, nothing is sent anywhere, and there is no sign-up.
This is a guide based on the numbers you enter. If you are not certain, send me a photo of the cylinder face and the door edge on WhatsApp and I will confirm the size for free before anything is ordered.
Common euro cylinder sizes
There is no single size that fits every door, which is exactly why measuring beats guessing. That said, most UK homes land on one of a handful of lengths, built from two halves in 5mm steps. The table below is the everyday range. Yours will almost certainly be one of these or a near offset of it.
| Overall length | Common split (A/B) | Typically found on |
|---|---|---|
| 60mm | 30/30 | Older or thinner doors; less common now |
| 70mm | 35/35 | Common on many uPVC doors |
| 80mm | 40/40 or 35/45 | Very common, symmetric or a slight offset |
| 90mm | 45/45 or 40/50 | Common offset on thicker doors |
| 100mm | 50/50 or 45/55 | Thicker composite doors |
Sizes are quoted as two halves measured from the central fixing screw, for example 40/50 (40mm outside, 50mm inside, 90mm overall). If your measurement falls between two standard sizes, pick the nearest that keeps the cylinder flush rather than proud.
Offset vs symmetric: getting the two halves right
This is the bit that trips people up when they buy a cylinder online. A symmetric cylinder has equal halves (40/40, 45/45). An offset cylinder has unequal halves (40/50, 35/45) because the cylinder does not sit dead-centre in the door. Most uPVC doors actually need a slight offset, and that is why two cylinders with the same overall length can both be "wrong" if the offset is back to front.
So always quote both halves, in order: outside face first, inside face second, by convention. A 40/50 and a 50/40 are the same overall length but mirror images, and fitting the wrong way round leaves the cylinder proud on the outside (a snap risk) and recessed on the inside. If your cylinder has a thumbturn, the turn goes on the inside and you still measure it the same way, just order it as a turn cylinder with the turn on that side. When in doubt, measure both halves, write them down outside-first, and either order to match or send me the two numbers and I will get the right one.
How to tell your cylinder is the wrong length
You do not need any tools to spot a badly-sized cylinder. Stand outside your front door and look at the brass cylinder face where it pokes through the handle:
- It sticks out past the handle by more than a few millimetres. Too long. The MLA guidance is no more than 3mm of protrusion, ideally flush. A proud cylinder is the single easiest target for a snap attack, so this is worth fixing even if the door still works.
- The key feels loose, or the cylinder rocks slightly in the door. Often a sign the cylinder is longer than the door needs and is not pulled up tight against the handle.
- The key will not always throw the bolt, or the door is hard to lock. Can mean the cylinder is too short, so the cam is not reaching far enough into the gearbox to drive the lock. (A key that will not turn at all is a different fault, covered on the key-won\'t-turn page.)
- It sits recessed, sunk behind the handle plate. Too short on that face, awkward to use and not driving the mechanism cleanly.
If any of those sound like your door, measure it with the steps above and order the right size, or send me a photo and I will tell you the size and whether it is worth a 3-star anti-snap upgrade while the cylinder is being changed anyway.
Recent cylinder-sizing jobs
Three recent calls across Wolverhampton, Stafford and Cannock, all down to cylinder size. One bought too long online, one needed measuring for an upgrade, one fitted too short by a previous trader. Real-pattern situations, real prices on the receipt, sat next to what a national number would have quoted. Customer details lightly anonymised at their request.
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Thursday 28 May 2026 at 10.30am · Wolverhampton
Mr Daniel F., Wolverhampton
Had bought a euro cylinder online by overall length alone and fitted it himself, but it stood out a good 8mm past the handle and the key felt loose. He rang worried it was insecure. It was: a proud cylinder is the snap-attack weak point.
A national number quoted the customer £140Paid to me £90Measured both halves properly, the offset was wrong (he had a symmetric cylinder where the door needed 40/50). Fitted a correctly-sized like-for-like that sat flush, and showed him the 3mm rule so he could check the back door himself. Standard hours, no call-out fee. Saved him the cost of a second wrong cylinder.
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Monday 18 May 2026 at 9.30am · Stafford
Mrs Carol W., Stafford
Wanted to swap a basic cylinder for a 3-star anti-snap but did not know what size to order. Sent me a photo of the cylinder face and the door edge on WhatsApp and I talked her through measuring it on the call.
A national number quoted the customer n/aPaid to me £90Turned out to be a 35/45. Brought the matching length, fitted a flush 3-star anti-snap in twenty minutes, and the part was itemised on the receipt for her records. She measured it herself in the end, I just double-checked. The right size first time, no guesswork.
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Saturday 23 May 2026 at 2.30pm · Cannock
Mr Habib R., Cannock
New cylinder a previous trader had fitted was too short and sat recessed, so the key would not always throw the bolt and the door sometimes would not lock. He thought the whole lock was failing. It was just the wrong length cylinder.
A national number quoted the customer £260Paid to me £170Out-of-hours weekend call. The gearbox and door were fine; the cylinder was simply 5mm too short on the inside half, so the cam was not reaching. Refitted the correct size and the door locked perfectly again. No new gearbox, no new lock body, just the right cylinder.
The link between cylinder protrusion and lock snapping is documented by the Master Locksmiths Association, which advises that a euro cylinder should not protrude more than 3mm from the handle. Secured by Design, the official UK police security initiative, makes the same point that the cylinder is the vulnerable part of the door and recommends cylinders certified to TS 007 or Sold Secure SS 312 Diamond to resist snapping. My from-price for a correctly-sized like-for-like cylinder supplied and fitted starts at £90, labour and a basic cylinder included.
What customers say about honest cylinder work
Verified Google reviews from real customers across Wolverhampton, Stafford, Cannock and the surrounding villages.
I was locked out of the house so gave Lockerfella a message. Sean was incredibly swift in his initial response, giving an ETA and an estimate cost at the same time. I immediately booked in with Sean and he came as arranged, tried his best to pick the lock, however it wasn’t to be so he changed the lock and was all done and dusted in a reasonable time. He was polite, prompt and professional. I would recommend anyone needing a locksmith to contact Lockerfella
Thankyou so much James. It was a pleasure to assist you in cannock that day with your emergency locksmith call-out.
I run a letting agency in Wolverhampton and unfortunately had a tenant whose UPVC locking system had collapsed locking them into the flat unfortunately during the football match between England and Croatia in the 2026 World Cup. As you can imagine, I was having a bit of trouble getting a locksmith! At least until Sean contacted me. He went out very quickly, opened the door and replaced the gearbox working from 11 pm until 2 am so not very sociable hours. Given that I thought the cost was very reasonable and the service was excellent. I will certainly be using Sean again and I cannot recommend him highly enough. The world of emergency locksmiths can be a murky one at times so it is really nice to have someone you can trust to call on.
Thankyou so much Andy. It wss my absolute pleasure. 😊
I had a great experience with Lockerfella Locksmith, especially with Mr Sean. He was professional, patient, respectful, and took the time to make sure everything was done properly. My door lock turned out to be much more difficult than expected, but Sean stayed calm and worked hard until the job was completed perfectly. I really appreciated his honesty, kindness, and excellent workmanship. I highly recommend Sean and Lockerfella Locksmith to anyone looking for a reliable locksmith. Thank you again, Sean, and I wish you continued success in your business!
It was an absolute pleasure helping you today Saeideh in Wolverhampton. Thankyou so much for the kind words. Sean - Lockerfella Locksmiths 24/7.
I locked myself out my house and phoned Sean at 1.32am. He arrived at my house in Bilston 35 minutes later. He lives 30 minutes away. He was very professional and tidy. I would recommend him to anyone. Within 1 hr and 15 minutes of calling him he had come out, sorted my lock and on his way home. You can call him anytime and he will get to you asap. Worthy of the 5 star rating
Thankyou for your review Shell. Real pleasure to assist you both with your emergency call-out. Sean - Lockerfella Locksmiths 24/7
Sean came out for an emergency call out at 2am due to a lock malfunction on the front door. He was responsive from the first point of the phone call and was clear with what he was able to do and provided an accurate timescale and live location When sean arrived he felt like someone who was a safe person and as a lone female that felt important when I couldn’t get in my home in the early hours. He’s was patient and thoughtful with my dogs who were trapped inside. He was friendly, calming and reliable. Would highly recommend him
Thankyou for your review, it means so much. I'm so glad I could help you this morning in Stafford with the emergency call out. Have a great day to you and the doggies 🐕. Sean - Lockerfella Locksmiths 24/7
Phoned this lovely man this morning before 8am , it's now 11.28 am and my lock is fixed , thank you Sean , as I live alone i was feeling vulnerable, thank you so much , fir your prompt response
Thankyou so much for your review Maureen. Real pleasure assisting you today in Walsall to replace your Euro Cylinder and Door handles. Sean ☺️
I contacted Sean in a panic after our back door wouldn’t lock at 21:15 on a Sunday night. Sean came back with a price almost immediately and offered to come and look at it straightaway. At my request, I asked him to come Monday morning and he sent me an ETA and turned up bang on time. Sean quickly diagnosed the problem, he had to go off to get a a part and when he was on his way back to me, he even shared his location via WhatsApp so I knew when he would be back. Part fitted, worksite cleaned up and he was on his way. Reasonably priced, fantastic communication from start to finish and a great bloke to speak too as well. Thanks Sean, you’re an absolute star!
Absolute pleasure meeting you and your wife today in Codsall / Wolverhampton. I'm really pleased I was able to repair your faulty upvc door mechanism. Thankyou for the glowing review....it's really appreciated. Sean - Lockerfella Locksmiths 24/7
Absolutely brilliant service from Lockerfella Locksmiths. We left Sean a whatsapp message at 2.30am as we had stupidly left our front door keys inside when leaving the house. He answered pretty much immediately. Sean arrived with us in Stafford within 30 minutes and had us back in within 5 minutes and fitted us with some upgraded anti snap locks. Thankyou!
You're more than welcome Matt 😊
Prices
From-prices for cylinder work
Measuring it yourself is free, and this guide is here so you can. If you would rather I supplied and fitted the right size, the figures below are the floor prices, attendance and labour included, with no separate call-out fee. I quote the all-in figure on the phone before I leave the van. The full price list with covers and affects sits on the dedicated pricing page.
- Standard euro cylinder supplied and fitted (correct size, like-for-like) from £90
- TS007 3-star anti-snap cylinder upgrade (labour the same, part itemised) from £130
- Out-of-hours emergency (6pm to 8am, weekends, bank holidays) from £170
No VAT added on top. No call-out fee. The from-price includes a standard cylinder; any anti-snap upgrade is itemised on the receipt with the standard it meets. See the full price list and what each one covers →
About the locksmith
The locksmith answering your call
I'm Sean Hamilton. I run Lockerfella as a one-man-band. If you are not sure what size cylinder your door needs, send me a photo of the cylinder face and the door edge on WhatsApp, or I will measure it on the doorstep, and I will fit the correct size there and then. The price is on the phone before I set off. No call-out fee. No upsell from a like-for-like cylinder to a brand or grade you do not need.
- 30+ years fascinated by locks. I've been picking, stripping and studying locks for the love of it for over 30 years. Lockerfella is what happens when a lifelong interest in how locks work becomes the day job.
- Trained and certified. Certificate of Locksmith Skills from A'Jam Locksmiths covering cylinder, mortice, padlock, wafer and euro lock picking, plus re-keying and mortice bypassing.
- Standard DBS checked, £1M insured, 12 months workmanship guarantee. Redacted DBS and insurance certificates are published on the About page, with originals available to view in person before work starts.
- One man, one van, one phone number. The phone rings on me directly. No call centre. No third-party fitter. If I quote you a price, that's the price you pay.
Common questions about euro cylinder sizes
Straight answers about what size you need, how to measure it, the common sizes, the offset that catches people out, and why a cylinder that sticks out is a security risk.
What size euro cylinder do I need?
You need the size that matches your door, and the only way to know it is to measure your existing cylinder rather than guess. A euro cylinder is sized by two measurements taken from the central fixing-screw point: the distance to the outside face (call it A) and the distance to the inside face (B). Add them for the overall length, and quote the two halves in their own right because most doors need an offset cylinder rather than a symmetric one. The single biggest mistake is buying by overall length alone and ending up with the wrong offset, so the cylinder either sticks out (a snap risk) or sits recessed (will not turn the cam). Measure both halves, write them down, and you will get the right part first time.
How do I measure a euro cylinder?
Measure from the centre, never from one end. The reference point is the central fixing-screw hole on the underside of the cylinder (the screw that holds it in the door). With a steel tape or a ruler, measure from the centre of that screw to the outside face of the cylinder, then from the centre of that screw to the inside face. Those are your two halves, A and B, and added together they give the overall length. Most cylinders come in 5mm steps, so if your measurement lands between sizes, choose the nearest standard size that keeps the cylinder as close to flush as possible. The step-by-step with a diagram is in the measuring section above.
What are the most common euro cylinder sizes?
In UK homes the most common overall lengths are 70mm, 80mm, 90mm and 100mm, made up of two halves in 5mm steps. A symmetric 35/35 gives 70mm, 40/40 gives 80mm, 45/45 gives 90mm and 50/50 gives 100mm. Offset cylinders are just as common because the cylinder often sits off-centre in the door: 40/50 and 35/45 are both everyday sizes. There is no single "standard" size that fits every door, which is exactly why measuring your own beats assuming. I carry the full common range of lengths and offsets on the van so I can match yours on the spot.
My cylinder sticks out past the handle. Does it matter?
Yes, and it is worth sorting. A cylinder that protrudes past the handle is the weak point a burglar exploits in a snap attack: the exposed section is gripped and broken off. The Master Locksmiths Association advises that a euro cylinder should not protrude more than 3mm from the handle, and ideally should sit flush with no overhang at all. If yours stands proud by more than that, it has been fitted too long. The fix is a correctly-sized replacement, and if you are changing it anyway it is usually the moment to step up to a TS007 3-star anti-snap cylinder for the same labour. The full anti-snap explainer is on the anti-snap locks page.
What happens if the euro cylinder is too short or too long?
Too long and the cylinder stands proud of the handle, which both looks wrong and creates the snap-attack weak point the MLA warns about. Too short and the cam in the centre will not reach far enough to drive the lock mechanism, so the key either will not turn or will not throw the bolt properly, and the cylinder can sit recessed where it is awkward to use. Either way the door does not work as it should and the lock is not as secure as it should be. The right size sits as close to flush as possible on both faces, which is why measuring both halves matters more than getting the overall length roughly right.
Do I measure a euro cylinder from the end or the middle?
From the middle. The fixing screw in the centre of the cylinder is the reference point, because that is where the cam sits and where the cylinder lines up in the door. Measure from the centre of that screw out to each face separately. Measuring end-to-end only gives you the overall length and tells you nothing about the offset, and the offset is what trips people up when they buy online. Centre to outside face, centre to inside face, written down as two numbers: that is the measurement a locksmith or a supplier actually needs.
Should I just get you to measure and fit the cylinder?
If you would rather not measure it yourself, that is exactly the sort of small job I am happy to do. Send me a photo of the cylinder face and the door on WhatsApp, or I will measure it on the doorstep, and I will fit the correct size there and then. A standard like-for-like euro cylinder supplied and fitted is from £90, labour and a basic cylinder included, no call-out fee and no VAT on top. If you want to step up to a TS007 3-star anti-snap at the same time, the labour is the same and I will quote the part on the phone. I would always rather measure twice and fit once than have you buy the wrong size online.
Ready when you are
Not sure of the size? Send me a photo on WhatsApp.
Snap the cylinder face and the door edge, send it over with your postcode, and I will tell you the size, whether it is sitting proud, and what a correctly-fitted replacement would cost. Or I will measure and fit it on the doorstep. No call-out fee. No deposit. No surprises.
Page last reviewed: . Reviewed by Sean Hamilton, the locksmith behind Lockerfella, under our editorial standards.