How to measure a lock cylinder to buy the right replacement

What you need

• Tape measure or, better, a vernier calliper
• Screwdriver for the faceplate screw
• Phone to photograph the cylinder with the tape alongside
• Paper and pen to note the measurements
• Replacement cylinder from Tesa, Abus, Ezcurra, Mottura or Yale, at Leroy Merlin, Bricodepot or a ferretería (hardware shop)

Step by step

1. 1

   Take the cylinder out if you can

   With the door open, loosen the faceplate screw level with the cylinder, insert the key, turn it about 15-20 degrees until the cam lines up and pull. Measuring the cylinder out of the door is the most accurate way. The full procedure is in how to change a lock cylinder.

2. 2

   Find the cam and the screw hole

   The cylinder is shaped like an elongated pear. At the bottom, at a point that is almost never the centre, is the threaded hole for the fixing screw, and directly above it the cam (the part that turns). That point is the reference for every measurement.

3. 3

   Measure from the outside end to the centre of the cam

   Put the calliper or tape on the end that faces the street and measure to the centre of the screw hole. Note the figure in millimetres. Normally 30, 35, 40, 45 or 50 mm.

4. 4

   Measure from the inside end to the centre of the cam

   Repeat from the other end, the one facing the inside of the home. The size is written outside/inside, for example 30/40. The sum is the overall length: 70 mm. A 35/35 cylinder also measures 70 but the screw falls in a different place, which is why you must give both figures.

5. 5

   If you cannot remove it: measure the door

   Measure the thickness of the door leaf and add the thickness of the escutcheon or rose on each side. The cam sits at the centre of the lock, which coincides with the centre of the leaf. So on a 45 mm door with a 10 mm outer escutcheon and a 5 mm inner rose, the cylinder is roughly 33/28, which you round to 35/30. Better 1-2 mm too long on the inside than on the outside.

6. 6

   Check the profile and the cam type

   In Spain almost everything is euro profile (pear shaped, 17 mm wide at the round part). Older aluminium doors and some security doors use a round or oval profile, and armoured doors may have a lever lock cylinder. The standard cam is 15 mm; if your lock is a clutch or knob type, note that too.

7. 7

   Decide whether you want a thumbturn or double clutch

   If the door is locked from inside with a turn and you open it often, a cylinder with an inside thumbturn saves hunting for the key. If you want to open from outside even when someone has left the key in on the inside, ask for double clutch. The measurements are the same.

8. 8

   Take a photo and go and buy

   Photograph the cylinder with the tape alongside or write down 30/40 euro profile standard cam. With that any ferretería will give you the replacement. If the exact size does not exist (for example 33/28), buy the next size up on the inside.

How to read lock cylinder sizes: table of common sizes

Cylinder sizes are always written as two numbers separated by a slash, outside/inside, in millimetres, measured from each end to the centre of the cam. Flat doors in Valencia and Alicante usually take 30/30, 30/40 or 35/35. Reinforced doors with a thick escutcheon go up to 30/50 or 35/55. Aluminium and uPVC terrace doors usually take 30/30 or 35/35 with a shorter cam.

There are two golden rules. First: the cylinder must sit flush with the outer escutcheon, never protrude more than 2-3 mm, because a cylinder that sticks out can be snapped with a pipe wrench in seconds. Second: if you are torn between two sizes, choose the one that leaves the excess inside the home, where it does not matter.

Mistakes when measuring and buying a cylinder

• Giving only the overall length. A 70 can be 30/40, 35/35 or 40/30. Without the offset, the screw does not line up and the cylinder wobbles or will not go in.
• Mixing up outside and inside. Fit a 30/40 the wrong way round and 10 mm sticks out on the street side. Always note which side faces out.
• Measuring with the escutcheon off. The outer escutcheon adds 8-15 mm. Measure with the escutcheons on, or add them.
• Not checking the cam type. Locks on aluminium doors and some multipoint locks need a short or clutch cam. A standard-cam cylinder goes in but does not move the bolt.
• Buying a cylinder without a security card for a front door. Without the card anyone can copy the key. Security cylinders come with an ownership card and copies are cut against it.

When to call a professional

Measuring and replacing a euro profile cylinder in a wooden door is a 10-minute job. If the door is armoured with a lever lock cylinder, if it has a security escutcheon that covers the cylinder and needs an exact size, if the old cylinder has snapped inside and will not come out, or if you are not sure of the cam type, it pays to let us do it: we carry the most common sizes and sort it in one visit.

A cylinder replacement costs 40-60 € in labour, plus the anti-bump cylinder from 35 €. Fixed price on WhatsApp from a photo of the door edge. If you are also locked out, opening the door costs 60-90 € between 8:00 and 21:00. Never drill a reinforced door to get out a cylinder that will not come: the bit will not go through the escutcheon and the door is left unusable.

More detail in locksmith in Valencia, Alicante and on the Costa Blanca and in how much it costs to change a cylinder and a lock. If it is the lock that is failing and not the cylinder, see how to change a door lock.

Which cylinder to buy on the coast

Size for size, in Torrevieja, Benidorm, Dénia or anywhere on the seafront choose a nickel-plated cylinder or one with an anti-corrosion finish. Untreated polished brass seizes with the salt air in 3-5 years and ends with the key snapped inside. Tesa TE5, Abus D6 and Ezcurra DS15 have finishes that hold up better; for reinforced doors, Mottura or Abus EC.

Always buy with 5 keys and a card, and if the property is a holiday let, think about a double clutch cylinder: that way you get in from outside even if a guest has left the key in on the inside. Lubricate with graphite when you fit it and every 6 months. If the old cylinder was stiff, read lock jammed: the cylinder will not turn before assuming the cylinder is to blame.