How do I measure a multipoint lock so the replacement fits?

Multipoint locks are not standardised. There are dozens of manufacturers and hundreds of variants, and a lock that is the right length may still have its hooks in the wrong place or its faceplate a few millimetres too wide for the routing in your door. The measurements below are the ones every supplier's selector asks for, in the order they ask.

Safety

What you'll need

• A steel tape or rule
• A vernier or digital caliper for the faceplate width (optional)
• A phone camera

Step by step

1. Photograph the faceplate markings first.Open the door and look along the steel strip on the closing edge. Most locks carry a maker's name and a reference number stamped or laser-etched into the faceplate, often near the gearbox. Photograph it straight on and in good light. If you can read it, the rest of the measuring is a check rather than the whole job.
2. Measure the overall length.Top of the faceplate to the bottom of the faceplate, including any extension tips beyond the fixing screws. Take it with the door open and the lock unthrown. This is the first thing every selector asks and it rules out most of the catalogue immediately.
3. Measure the faceplate width.Across the flat steel strip, not across the door edge. The common domestic widths are close together, so use a caliper if you have one. A faceplate wider than the routing in the door will not sit flush; a narrower one leaves a gap and does not support the case.
4. Measure the backset.From the front face of the faceplate, straight back into the door, to the centre of the cylinder hole. This sets how far in from the door edge the keyhole and handle sit, and it cannot be changed.
5. Measure the PZ.From the centre of the square spindle hole to the centre of the cylinder hole. On domestic uPVC doors this is very commonly 92mm, with 62mm the main alternative. It has to match your handle as well as your door, so check both.
6. Measure from the gearbox to the first bolt each way.Centre of the spindle hole up to the centre of the nearest bolt above it, and down to the centre of the nearest bolt below it. Two locks of identical length and PZ can have completely different bolt spacings, and the keeps in your frame are already cut to your spacing.
7. Note the bolt types and their order.Write down what each bolt is, in order from the top: hook, roller, deadbolt, latch. A hook-and-roller lock and an all-roller lock of the same size are different parts and will not use the same keeps.
8. Note the faceplate end shape.Square, or radiused with a curved end. The routing in the door edge was cut to one or the other. A radiused faceplate in a square routing leaves visible gaps at both ends.
9. Measure the door thickness while you are there.You will need it if the cylinder or the handle is being changed at the same time, and you will almost certainly want to change the cylinder if the door is old enough to need a lock.
10. Check whether the lock is handed.Some hooked locks are made in left and right versions and cannot be reversed; others have reversible hooks or a latch that can be turned over. Ask before ordering, and describe the door in words as well as by a code.

Tips

• If the lock is obsolete, ask specifically about a universal or adaptable replacement. Several manufacturers make locks with an adjustable gearbox position or supplied with alternative faceplates, made precisely for this situation.
• Take the measurements to a dedicated hardware supplier rather than a general merchant. The people who sell these parts every day can often identify a lock from one good photograph.
• If you cannot identify it and the door is under ten years old, the door's own manufacturer will often name the lock from the frame's kitemark label or the guarantee paperwork.

Common mistakes

• Measuring the door instead of the lock — Doors of the same height take many different lock lengths. The lock length has to match the lock, and nothing about the door tells you what it is.
• Ordering on length and PZ alone — Those two figures are shared by dozens of locks with different bolt spacings. If the hooks land between your keeps, the new lock is useless and the frame has to be re-cut.
• Removing the old lock to measure it before ordering — The door then cannot be locked, and a discontinued lock can take weeks to source. Measure in place, order, and only strip the door when the part arrives.

Questions people ask