Lock Shop Direct measurement guide
How to Measure a Mortice Lock or Latch
This guide explains how to identify and measure mortice locks, sashlocks, deadlocks, bathroom locks and latches before ordering a replacement.
Important: Do not rely on the size of the hole in the door. Where safe, remove and measure the existing lock body, then compare every measurement and operating feature.
1. Identify the mortice product
Mortice products are fitted into a pocket cut into the edge of a timber or metal door. Identify whether the existing item is a latch, deadlock, sashlock, bathroom lock or cylinder-operated lock case before comparing sizes.
Tubular or mortice latch
Latch bolt only, operated by a handle. Record backset, case size and forend.
Deadlock
Deadbolt only, operated by a key or cylinder. Record key or cylinder profile and case dimensions.
Sashlock
Latch and deadbolt together. Also record the vertical centres between the spindle and keyhole or cylinder.
Bathroom lock
Latch and privacy deadbolt, usually with a separate turn. Record centres and follower sizes.
Euro or oval lock case
Operated by a removable profile cylinder. Match the cylinder cut-out and cam operation.
Rebated lock
Used on a pair of rebated doors. Check whether a matching rebate kit is fitted and its depth.
2. Take the main lock measurements
Remove the handles and lock only where it is safe to do so. Measure the metal lock case rather than the cut-out in the door, because old mortices can be oversized or altered.
| What to check |
How to measure or identify it |
Record |
| Backset |
Edge of the forend to the centre line of the spindle, keyhole or cylinder. Use the same reference shown on the product page. |
_____ mm |
| Case depth |
Rear of the forend to the back of the lock body, excluding the forend. |
_____ mm |
| Case height |
Top to bottom of the lock body. |
_____ mm |
| Forend length |
Top to bottom of the faceplate. |
_____ mm |
| Forend width |
Across the faceplate. |
_____ mm |
| Centres |
For a sashlock or bathroom lock, centre of spindle to centre of keyhole, cylinder or turn follower. |
_____ mm |
3. Check the operational details
- Keyhole, euro cylinder, oval cylinder or bathroom-turn cut-out.
- Latch and deadbolt positions and the direction of the latch bevel.
- Whether the latch is reversible or the lock is handed.
- Spindle follower size and whether the lock uses one or two followers.
- Faceplate shape: square or radius ends.
- Faceplate finish and the position of the fixing screws.
- Number of levers, security standard or certification where required.
- Whether the existing keep, strike plate or rebate kit must also be replaced.
4. Measure the keep and door preparation
If the new lock is not an exact model-for-model replacement, measure the keep or strike plate and check its relationship to the latch and deadbolt. Record the door thickness, frame material and whether the door pair is rebated.
Existing fixing holes can be useful, but they are not a reliable substitute for the lock dimensions. Manufacturers may change screw positions between ranges.
5. External, fire and escape doors
Safety-critical doors: If the lock is fitted to a fire door, final exit, communal entrance or other controlled door, match the required certification and the door-set specification. Do not alter the door or substitute components solely because the dimensions appear similar.
For an external entrance door, also check any insurance or security requirement before selecting a replacement. The standard, lock type and compatible door furniture may matter as much as the measurements.
Still not sure which product you need?
Send our team clear photographs and your measurements before ordering. Please include:
- Photographs of both faces of the lock and the complete forend.
- Backset, case depth, case height, forend length and width.
- Centres between the spindle and keyhole, cylinder or turn.
- A photograph of the keyhole or cylinder cut-out and latch/bolt layout.
- Any brand, case stamp, standard mark or product number.
This guide is intended to help identify and measure replacement hardware. Product designs, terminology and handing conventions can vary by manufacturer. Always compare the complete product specification and fitting instructions. Where a door or fitting forms part of a fire escape, fire door, powered system or other safety-critical installation, obtain advice from a competent person before ordering or altering the hardware.