60mm vs 70mm Backset: The Measurement That Decides If a Smart Lock Fits

Of every return or exchange we deal with, the single most common cause is the same: someone ordered a lock in the wrong backset. It's an easy mistake to make, because "backset" isn't a term most people have ever needed to know, and the two sizes our lever locks come in — 60mm and 70mm — look identical if you're not specifically measuring for them. Get this one number right and everything else about choosing a lock gets simpler. Here's exactly what it means and how to check yours in under a minute.

What Backset Actually Measures

Backset is the horizontal distance from the edge of the door — the part that meets the frame when closed — to the centre of the hole where your existing handle or lock sits. It has nothing to do with the door's overall width, its thickness, or its height. It's purely about where the handle hole sits relative to the door's edge, because that's what determines whether a new lock's internal latch mechanism reaches the strike plate on the frame correctly. Two doors can look identical from the outside and still have different backsets, because it comes down to how the door was manufactured, not how it looks.

It helps to picture what's actually inside the door at that point. A standard hinged door has a rectangular cavity — the mortise — cut into its edge, sized to hold the latch mechanism itself, and a round bore hole drilled through the face of the door for the handle spindle to pass through. The backset is simply the distance between those two things: the door's edge and the centre of that bore hole. Every lock manufacturer machines their latch mechanism to a specific length matching one backset measurement, because the latch bolt has to travel exactly that far to reach past the door's edge and into the strike plate recessed in the frame. Get the backset wrong and you're not dealing with a lock that's slightly awkward to fit — you're dealing with a latch mechanism that is physically the wrong length for the cavity it needs to sit inside.

60mm vs 70mm: Both Exist for a Reason

Unlike some sizing questions where one option is rare, 60mm and 70mm backsets both turn up on hinged doors — there's no shortcut of "just assume 60mm and you'll probably be right." Older doors, doors from certain builders, and doors on some project-home ranges lean one way or the other without any visible pattern from the outside. The only reliable way to know which you have is to measure the door you're actually replacing hardware on, every time, even if a neighbouring door in the same house turned out to be the other size.

This last point trips people up more than any other: it is genuinely common for a single house to mix backsets across different doors, particularly if a front door was replaced at some point without matching the original hardware standard, or if a renovation added a side entry from a different supplier than the one that built the rest of the house. Measuring the front door and assuming the laundry door, side gate or garage entry door share the same backset is a real source of the wrong-part orders we see. If you're planning to fit smart locks to more than one door, treat each one as its own measurement job rather than copying a number across the whole property, even when the doors look like they came from the same original batch.

What Happens If You Order the Wrong One

This isn't a case of "it'll be a bit loose" or "you can force it." A lock ordered for the wrong backset has its internal latch mechanism positioned at the wrong distance from the mounting plate — the latch simply won't reach where the strike plate on the door frame is, or the handle spindle won't line up with the existing hole at all. There's no adjustment on-site that fixes a backset mismatch; the only options are returning for an exchange or, in rare cases, modifying the door itself, which we don't recommend and don't cover under warranty. Measuring correctly before ordering is genuinely the only step that matters here.

It's worth understanding why the mismatch is absolute rather than a matter of degree. The latch bolt inside a smart lock travels along a fixed track from the edge of the door to the strike point, and that track is machined to one specific length during manufacturing — there's no slack built in for a few millimetres either way, because the mechanism also has to line up internally with the keypad, motor and battery housing packed into the same handle assembly. A backset that's even 10mm off means the latch bolt either can't extend far enough to reach the strike plate cut into the frame, or the handle spindle hole doesn't line up with where your existing door prep already has a hole cut through it. Neither of those is something a screwdriver fixes on the day.

✓ 60mm, 70mm or adjustable

Smart Door Lock — Fingerprint & Code

Choose your exact backset, or the adjustable 60–70mm version if you're not certain which one you have.

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The Adjustable Option: One Lock That Fits Both

If measuring feels like a step you'd rather skip, or you genuinely can't tell from the existing hardware which backset you have, our Adjustable Latch lever lock (SL-H2) ships with a latch built to cover the full 60–70mm range, adjusted during installation rather than committed to before you order. It removes the single biggest source of measurement error entirely — you still need to confirm the door itself is a standard hinged timber door within that range, but the specific 60 vs 70 decision stops being something you have to get exactly right in advance.

For a tradesperson fitting multiple units across a job site with doors from different eras or suppliers, that flexibility also means carrying one SKU instead of two — a practical win for installers as much as for a homeowner unsure of their own measurement. It's the same reason we recommend the adjustable version by default to anyone who hasn't measured yet, rather than asking them to guess and risk an exchange.

✓ Adjustable latch included

Smart Door Lock — Lever Handle, Adjustable 60–70mm

One latch covers both backsets — measure less, worry less about ordering the wrong one.

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Explore the Full Range

If your door is a narrow aluminium or glass-framed stile rather than standard timber, backset isn't the right measurement at all — check our sizing guide for the centres system used on those doors instead. And if you're still deciding on entry method or app before you even get to fit, our guides on fingerprint vs keypad code and TTLock vs Tuya cover those decisions.

Frequently Asked Questions

How do I measure my door's backset myself?
Measure from the edge of the door (where it meets the frame when closed) to the centre of your existing handle or lock hole. Our sizing guide shows exactly where to place the tape with diagrams.

What if I can't tell whether my door is 60mm or 70mm?
Measure carefully first — it's usually a clear, precise number once you do. If you genuinely can't be certain, our adjustable-latch SL-H2 covers both without you needing to commit in advance.

Can I install a 60mm lock on a 70mm backset door, or vice versa?
No. The internal mechanism is built for a specific distance and won't line up correctly if it's wrong — this isn't a tolerance you can force or adjust on-site.

Does backset apply to narrow aluminium or glass doors too?
No. Those doors use a different measurement called centres, not backset. Don't apply the 60/70mm standard to a narrow-stile door — check the sizing guide for the correct system.

What does a code like "6085" on a push/pull lock mean?
It's backset followed by centres — 6085 means a 60mm backset with 85mm between centres. Reading it that way lets you decode any of our mortise codes without a lookup table.

What happens if I order the wrong backset by mistake?
Contact us for an exchange before attempting to install — the lock's mechanism won't physically line up, and there's no on-site fix. We'd rather swap it than have you force an install that damages the door.

Key Takeaways

• Backset is the distance from the door edge to the centre of the handle hole — measure every door individually, never assume.
• Both 60mm and 70mm turn up on UK doors; there's no safe default to guess.
• A wrong backset simply won't install — there's no on-site adjustment, only an exchange.
• SL-H2's adjustable 60–70mm latch removes this risk entirely if you're unsure.
• Narrow aluminium or glass doors use centres, not backset — a different system entirely.
• Browse the full range in Smart Door Locks, or check the sizing guide before ordering.