Smart Lock Sizing Guide
Nearly every smart lock that goes back in the box goes back for the same reason: it did not fit. This page exists so that does not happen to you. Work through it once, with a tape measure, and you will know exactly which product and which option to order.
The short version. Find your door type below, take the one or two measurements it asks for, and match them to the option on the product page. If at any point you are unsure, stop and email us a photo of your door edge with a tape measure laid across it — we answer within a business day and it costs you nothing.
1. Start with your door, not the lock
Every measurement that follows depends on what kind of door you have. Find your column.
2. The four measurements
You will not need all four for every lock, but you should know what each one is. All four are shown on the same diagram.
Backset — the one that matters most
Open your door and look at the flat face. There is a round hole the handle passes through. The backset is the distance from the edge of the door to the centre of that hole.
In Australia this is almost always 60 mm. On wider stiles and in older homes it is sometimes 70 mm. If you measure 45 mm or 50 mm, you have a European or imported fitting — tell us before you order, because most of our lever locks will not go on it.
- Open the door fully so you can see the flat face and the edge at the same time.
- Hook the tape on the edge of the door, not on the door frame and not on the edge of the lock plate.
- Read to the centre of the round hole, not to its near edge. That is where people lose 25 mm.
- Write it down and photograph the tape in place. If you email us later, that photo answers most of our questions.
Door thickness
Measure the edge of the door. Australian entry doors are usually 35 mm or 40 mm. Our lever locks go down to 35 mm; the face-recognition lock starts at 40 mm and will not suit a 35 mm door. This is the measurement that catches people out at the top of the range.
Borehole diameter
The width of the round hole itself, usually 50–54 mm on an Australian door. If yours is smaller, the hole needs enlarging with a hole saw. If it is much larger, the lock body may not cover it and you will see daylight around the edge.
Stile width
The vertical rail of the door — the solid timber or aluminium running down the lock side. Nobody thinks to measure this and it is genuinely eliminating: below roughly 96 mm, the lock body will not physically fit no matter what else matches.
| Backset | Minimum stile width | Typical door |
|---|---|---|
| 28 mm | Around 50 mm | Narrow aluminium, framed glass, sliding |
| 35 mm | Around 60 mm | Aluminium framed, apartment entry |
| 45 mm | Around 86 mm | European and imported doors |
| 60 mm | 96 mm | Standard Australian hinged timber |
| 70 mm | Around 106 mm | Wide stiles, older Australian homes |
3. Reading the mortise code
On the push/pull and sliding-door locks, every option carries a four-digit code. It is not a style name — it is two measurements stuck together.
Backset first, centres second. 6085 means a 60 mm backset with 85 mm between the centre of the square spindle and the centre of the key cylinder. 4585 is the same spacing on a 45 mm backset — a European fitting that will not go on a normal Australian door.
Hook bolt or straight bolt?
A straight bolt slides out sideways into the jamb. That works on a door that swings. On a door that slides, there is nothing for it to slide into — so a sliding door needs a hook bolt, which swings out and hooks around the keep. If your door runs on a track, you want the option with "hook bolt" in the name, in whatever backset you measured.
4. The measurement your lock actually needs
| If you are buying | Measure | Then order |
|---|---|---|
| Lever handle lock SL-H1 / SL-H2 |
Backset, door thickness, stile width | 60 mm, 70 mm, or the 60–70 mm adjustable latch |
| Push/pull, long handle SL-P1 |
Mortise backset, door thickness | 6085 for a standard Australian door, otherwise match your code |
| Sliding / narrow stile SL-P2 and SL-P2-S |
Mortise backset, and whether the door slides | The hook bolt version of your backset if it slides |
| Camera lock SL-C1 |
Confirm 22 mm backset, then spindle-to-cylinder centres | 22 × 147 up to 22 × 240 mm |
| Face recognition SL-F1 |
Backset and thickness — thickness is the catch | Single 6068 configuration, doors 40–90 mm |
| Outdoor gate SL-G1 |
Gate thickness and the width of its flat face | Single configuration, 20–65 mm thick, 34 mm panel |
5. Questions people actually ask
Measuring
I measured 57 mm. Is that 60 mm?
Almost certainly yes. Backsets are manufactured to standard sizes and a tape measure held against a painted door will read a couple of millimetres either way. Anything between 55 and 63 mm is a 60 mm backset. If you genuinely land halfway between 60 and 70, order the adjustable latch and stop worrying about it.
Do I measure to the edge of the hole or the centre?
The centre. Measuring to the near edge of the hole is the single most common mistake and it makes a 60 mm backset read as about 35 mm — which would send you to completely the wrong product.
Do I include the lock plate in the measurement?
No. Measure from the bare edge of the door itself. If a metal faceplate wraps around the edge, measure from the outer face of that plate — it is only a millimetre or two and it is what the manufacturer measures from.
My door has no lock in it yet. What do I measure?
Then you get to choose. Cut the hole at a 60 mm backset and you will be able to fit almost anything sold in Australia for the next twenty years. Tell us it is a fresh door and we will send you the drilling template before you cut.
What if my two doors measure differently?
That is common in a house that has been renovated in stages. Measure each door separately and order accordingly — or order the adjustable latch for both and keep it simple.
How do I measure the centres on a narrow stile door?
From the centre of the square handle spindle to the centre of the key cylinder, on the lock you already have. Both are visible on the face of the door. That number is the second half of the code — 147, 160, 170, 180, 190 or 240 mm.
Fitting
Can I fit it myself?
If you are replacing a like-for-like lock and your existing hole already matches the backset, yes — a drill, a screwdriver and the supplied template will do it in under an hour. Every lock comes with instructions and all the hardware.
If you are cutting a fresh hole, changing mortise size, or the latch pocket needs deepening, get a locksmith. It is an hour of their time and the result will be square.
What is the difference between a mortise and a latch?
A latch is a simple tubular bolt that slides into a hole drilled through the edge of the door — the standard Australian residential fitting. A mortise is a rectangular steel box that sits in a pocket cut into the door edge, carrying the bolt, the spindle and the cylinder together. Mortises are more common on aluminium, apartment and commercial doors.
You cannot swap one for the other without cutting the door. Match what you already have.
Will the new lock cover the old holes?
Usually, and that is why like-for-like is easy. If you are moving from a small knob set to a full lever plate you will almost certainly cover more, not less. Moving the other way is where you get visible marks — send us a photo of the existing door face and we will tell you before you buy.
Do I need to change the strike plate?
Sometimes. Australian jambs are often already cut for a Lockwood strike, and the supplied strike may need a small adjustment to the recess with a chisel. It is minor work and the instructions cover it.
Left-hand or right-hand door — which do I order?
Neither. Every lock we sell is handed reversible, so one product fits a door hung either way. The instructions show you how to set it during installation.
Can I put a smart lock on a fire door or an exit door?
No. Nothing in our range is certified for fire doors or required exit doors. Both are governed by specific Australian standards and need certified hardware. Do not fit these locks to either.
What about a security screen door?
Not from our current range. An Australian security screen door has a very narrow stile and needs a dedicated lock. We would rather say no than sell you something that does not suit it.
Choosing between our locks
My front door gets rained on. Which lock?
Only the ones rated IP66: the SL-G1 outdoor gate lock and the SL-P1 / SL-P2 push/pull range. Everything else in the range carries no published weather rating and belongs under an eave, a porch or a roof.
A smart lock is a circuit board in a metal case. This is not a detail to guess at.
SL-H1 or SL-H2 — what is the real difference?
The SL-H1 is cheaper, has a built-in doorbell and more narrow-stile options. The SL-H2 costs more and includes the 60–70 mm adjustable latch in the box, so there is no wrong size to order, and it handles far more users — 9 administrators and 291 users against the SL-H1's smaller capacity.
If you know your backset, the SL-H1 is better value. If you would rather not measure precisely, pay the difference for the SL-H2.
Long handle or short handle on the push/pull?
Long for full-width timber and framed glass doors, where there is room for a proper grip. Short for narrow aluminium stiles and sliding doors, where a long lever would foul the frame. The electronics are identical.
Do I need the camera lock or a separate camera?
The camera lock is a video peephole you can read from your phone — check a delivery, see who knocked, look before you open. It is not a security camera system: no continuous recording, no cloud plan. If you want footage kept and searchable, buy a camera as well as a lock, not instead of one.
Can I unlock the door when I am not home?
Depends on the model. The SL-C1 has Wi-Fi built in and does it out of the box. The rest are Bluetooth and reach only a few metres — they need a gateway plugged in near the door, sold separately, before anything works remotely. Each product page says which.
Does any of this work with Apple Home?
No. Our range runs on TTLock and Tuya, which support Amazon Alexa and Google Assistant through a gateway. There is no Apple Home or Matter support, and we would rather you knew that now than after delivery.
If it goes wrong
I ordered the wrong size. What now?
Contact us. We would far rather swap the mortise than leave you with a lock you cannot fit. Tell us what you measured and what you received, and send a photo of the door.
The lock arrived and the hole does not line up.
Stop before you drill anything. Photograph the door face, the door edge with a tape measure, and the lock next to it. Email us all three. Most of these are solved by swapping one part, not the whole lock.
What happens if the batteries die while I am out?
Two ways in. Every lock ships with mechanical keys — keep one somewhere sensible that is not inside the house. And most models have a USB emergency port on the outside: touch a phone power bank to it and the keypad wakes up long enough to let you in.
How long do the batteries last?
Around twelve months of normal household use on the models that publish a figure. Heavy traffic, very cold weather and a constant Wi-Fi connection all shorten it. The lock warns you well before they go — act on the first warning, not the fifth.
Still not sure?
Then do not guess, and do not order. Send us three photographs and we will tell you exactly what to buy:
- The edge of your door with a tape measure laid across it
- The face of your door around the existing lock
- The existing lock or mortise itself, if you can get it out
We answer within one business day. It takes us two minutes and it saves you a return.
Email us your door photoscontact@flashmarques.com — we will tell you which product and which option to order