How to Measure a Storefront Lock: Backset, Door Thickness, Bolt Type, and Door Handing
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Before replacing a storefront lock, measure the existing lock—not just the door. Record the backset from the manufacturer’s door-edge or faceplate reference to the lock operating center, measure the structural door thickness in a different direction, identify the bolt or latch, document door handing and interior hardware, and photograph the existing holes, frame, strike, or bottom rail. These measurements work as a set; one matching number does not confirm compatibility.
Quick Answer: What Must Be Measured?
| Check | Measurement or evidence | Why it matters |
|---|---|---|
| Lock-body category | Deadlock, deadlatch, or bottom-rail lock | These categories are not interchangeable |
| Backset | Door-edge or faceplate reference to the specified lock centerline | Selects the correct lock-body configuration |
| Door thickness | Across the structural door section, face to face | Determines whether the trim and fasteners can span the door |
| Bolt or latch | Hookbolt, straight deadbolt, or spring-loaded deadlatch | Must work with the existing frame, strike, or receiver |
| Door operation | Swinging or sliding; hinge or pivot side; push or pull; reference side | Prevents ambiguous left-hand or right-hand descriptions |
| Interior hardware | Knob, thumb turn, push paddle, or bottom-rail operator | Helps confirm the operating arrangement |
| Existing preparation | Faceplate, holes, trim footprint, frame, strike, threshold, or floor receiver | Determines whether the site preparation can support the candidate lock |
| Special systems | SFIC core, keyway, pin count, and keying requirement when applicable | Door fit and key-system fit are separate decisions |
If you have not yet identified the lock-body category, use the storefront lock identification guide before measuring.
Tools and Photo Checklist
Keep the door open and stable while documenting the hardware. Use:
- A rigid ruler or tape measure with clear inch markings.
- A caliper for smaller dimensions when it can be used safely.
- A phone or camera for full views and close-ups.
- A printed or digital measurement record.
- A pencil or removable marker for noting reference points without damaging the door.
Take every measurement twice. Photograph the ruler in place with both the start point and end point visible. Keep the camera square to the measurement so perspective does not distort the result. Do not estimate an actual dimension from an unscaled photo, and do not place hands near hinge, pivot, latch, or door-closing pinch points.
A Seven-Step Storefront Lock Measurement Process
| Step | Action | Record |
|---|---|---|
| 1 | Identify the lock-body location and action | Deadlock, deadlatch, or bottom rail; swinging or sliding door |
| 2 | Find the correct backset reference | Exact start point and operating center shown by the current lock or model diagram |
| 3 | Measure backset | Inches and millimeters, plus a photo with the ruler |
| 4 | Measure structural door thickness | Face-to-face thickness, excluding trim unless the model diagram says otherwise |
| 5 | Identify the bolt and receiver | Hookbolt, straight deadbolt, or spring latch; strike, jamb opening, threshold, or floor receiver |
| 6 | Record handing and interior hardware | Reference side, hinge or pivot side, push or pull, keypad side, and inside operator |
| 7 | Document the existing preparation | Faceplate, holes, frame, strike, rail, threshold clearance, labels, and SFIC requirements |
Do not order from the table alone. The dimensions must be compared with the exact product configuration and its current installation instructions.
How to Measure Storefront Lock Backset
Backset is the horizontal distance from the door-edge or faceplate reference specified for the lock to the lock’s operating centerline. On many narrow-stile storefront preparations, that centerline aligns with the cylinder opening or spindle location. However, the start point and center point must follow the diagram for the existing lock and the candidate model.
Backset measurement steps
- Open the door and photograph the door edge, faceplate, exterior operator, and interior hardware.
- Locate the operating center shown in the existing lock’s technical drawing. If the visible cylinder hole is the stated reference, use its center—not the edge of the trim.
- Locate the vertical door-edge or faceplate plane used by that same drawing.
- Hold the ruler perpendicular to the door edge and measure to the centerline.
- Record the exact reading in inches and millimeters, the start and end references, and the source diagram used.
- Repeat the measurement and photograph the ruler square-on.
Current EASILOK product information lists these backset directions for relevant narrow-stile deadlock and deadlatch configurations:
| Nominal backset | Approximate metric equivalent | Ordering rule |
|---|---|---|
| 31/32 inch | 24.6 mm | Confirm the exact model and configuration |
| 1-1/8 inches | 28.6 mm | Confirm the exact model and configuration |
| 1-1/2 inches | 38.1 mm | Confirm the exact model and configuration |
Some existing locks—including Adams Rite MS1850S configurations—may have a 7/8-inch backset. EASILOK’s current SK1850 catalog does not list 7/8 inch, so do not round or substitute 31/32 inch.
Do not round a field measurement to the closest option until the reference points and existing lock preparation have been verified. Availability must be checked by model and current configuration; the table does not mean every option is available for every SKU.
How to Measure Narrow-Stile Door Thickness
Door thickness is measured across the structural door section from one door face to the opposite door face. It is not measured from the door edge to the lock center. When possible, measure at an exposed edge near the lock without including surface-mounted trim, keypad housings, pull plates, weather seals, or decorative caps—unless the model-specific drawing explicitly includes them.
For relevant EASILOK narrow-stile deadlock and deadlatch families, the catalog lists a door-thickness direction of 1-3/8 to 1-3/4 inches, approximately 34.9 to 44.5 mm. This range is only one fit condition. The lock-body category, backset, bolt or latch, holes, frame, strike, handing, and exact configuration must also match.
A storefront lock for a 1-3/8-inch door or a storefront lock for a 1-3/4-inch door is therefore not selected by door thickness alone.
Identify the Bolt or Latch Before Selecting a Lock
Record the shape, motion, and receiving hardware of the existing locking part.
| Existing locking part | What to observe | Related site evidence |
|---|---|---|
| Hookbolt | A rigid hook-shaped bolt that projects and hooks into its receiver | Hook orientation, receiver shape, door movement, frame or jamb |
| Straight deadbolt | A rigid straight bolt that projects into a prepared strike or jamb opening | Bolt dimensions, throw direction, strike or jamb preparation |
| Deadlatch | A spring-loaded latchbolt used with a matching strike and commonly an interior paddle in this application | Latch bevel or orientation, strike, paddle, frame, closing action |
| Bottom-rail mechanism | Locking action at the lower rail and threshold or floor receiver | Rail geometry, old-lock area, threshold, floor receiver, clearance |
Never substitute a preferred bolt type for the existing preparation without a qualified fit assessment. A hookbolt, straight deadbolt, and spring-loaded deadlatch have different operating relationships with the door and receiver.
If the shape or action is unclear, return to the deadlock, deadlatch, and bottom-rail identification guide.
Record Door Handing and Interior Hardware
Handing terms can vary by manufacturer and by whether the observer is on the secure side, outside, push side, or pull side. Avoid sending only “left-hand” or “right-hand.” Create an observable record:
- State the reference side—for example, “standing outside on the keypad side.”
- Record whether the hinges or pivots are on the left or right from that side.
- Record whether the door swings toward or away from the observer, or whether it slides left or right.
- Photograph the full door from both sides.
- Photograph the interior operator: knob, thumb turn, push paddle, or bottom-rail operator.
- Compare those facts with the exact model’s current handing diagram before configuring the tailpiece or latchbolt.
For example, current EASILOK documentation shows a 90-degree tailpiece adjustment for SK1850S(sfic) and SM1850, while SK4510S(sfic) has a reversible latchbolt and a non-handed push paddle. Those features do not eliminate the need to document the actual door and follow the exact installation instructions.
Record the Existing Holes, Faceplate, Frame, and Strike
A matching backset can still lead to a poor fit if the surrounding preparation differs. Photograph and measure, where the relevant technical drawing provides a basis:
- Faceplate length, width, shape, screw positions, and orientation.
- Cylinder, spindle, or trim openings and their center-to-center relationships.
- Exterior and interior trim footprint.
- Door-edge cutout and any visible modifications.
- Frame or jamb condition.
- Strike or receiver position, dimensions, and alignment.
- Door clearance and whether the door closes normally without force.
Do not assume a replacement will be drill-free because a model name, backset, or exterior appearance matches. A no-drill result is possible only when the existing lock body, preparation, backset, door thickness, bolt or latch, frame, strike, and other relevant conditions match the candidate configuration.
Special Checks for Glass-Door Bottom-Rail Locks
A bottom-rail lock requires a separate measurement path. Glass-door bottom-rail lock dimensions must describe the rail and old-lock geometry, threshold or floor receiver, clearance, and access—not only the glass. Do not use the narrow-stile backset table as a universal bottom-rail selector, and do not treat a catalog “thickness” value as the glass thickness.
Record:
| Bottom-rail check | Evidence to capture |
|---|---|
| Existing lock identity | Brand, model marking, old-lock face, access points, and full rail location |
| Rail construction | Rail width, height, profile, and the old-lock opening based on a model-specific diagram |
| Threshold or floor receiver | Position, dimensions, alignment, and available clearance |
| Removal path | How the old lock can be accessed and removed without giving unverified disassembly instructions |
| Door movement | Swing or pivot behavior, clearances, and any abnormal contact |
| Keying requirement | Cylinder or SFIC need, plus the actual core, keyway, pin count, and keying specification |
EASILOK SK777 and SK777S(sfic) follow the bottom-rail path associated with CRL 777S, FHC R777, and ILCO BRL references, subject to field verification. The reference model name does not prove that the rail, threshold, old-lock dimensions, or removal path match.
If the old bottom-rail lock cannot be accessed without moving the glass door, or if the rail, glass, pivot, threshold, or removal path is uncertain, stop and ask a qualified glass-door or lock professional to inspect it.
Storefront Lock Measurement Record Template
Copy this table into an email or work order. Write “unknown” rather than guessing.
| Field | Your record |
|---|---|
| Door location / ID | |
| Full-door operation | Swing / slide; push / pull; hinge or pivot side |
| Observation side used | |
| Existing lock-body category | Deadlock / deadlatch / bottom rail / unknown |
| Existing brand and model marking | |
| Backset | ___ in / ___ mm; start: ___; end: ___ |
| Structural door thickness | ___ in / ___ mm; exclusions: ___ |
| Bolt or latch | Hookbolt / straight deadbolt / spring latch / unknown |
| Interior hardware | Knob / thumb turn / push paddle / rail operator / other |
| Faceplate and holes | Dimensions and photo filenames |
| Frame, strike, or receiver | Condition, dimensions, and photo filenames |
| Bottom rail and threshold, if applicable | Rail size, clearance, old-lock area, removal path |
| SFIC, if applicable | Core format, keyway, pin count, keying requirement |
| Candidate model/configuration | |
| Person who verified the record |
Attach full-door, outside, inside, door-edge or rail, bolt or latch, receiver, label, and ruler-based measurement photos.
Common Measurement Mistakes
| Mistake | Why it fails | Correction |
|---|---|---|
| Treating backset as door thickness | They run in different directions and answer different fit questions | Photograph and label both dimensions separately |
| Measuring from the trim edge | Decorative trim may not be the technical reference | Follow the existing and candidate model diagrams |
| Choosing by the old model name alone | Parts and preparations may have changed | Verify lock body, dimensions, bolt, holes, frame, and receiver |
| Rounding an unclear photo measurement | Perspective and hidden reference points can change the result | Use a physical ruler, visible endpoints, and a square-on photo |
| Ignoring the strike or frame | The bolt or latch must engage matching receiving hardware | Record receiver type, position, condition, and alignment |
| Calling a catalog bottom-rail value “glass thickness” | Rail construction and glass thickness are not the same measurement | Measure the rail, threshold, old-lock area, and removal path |
| Assuming matching dimensions mean drill-free installation | Hidden holes, cutouts, trim, or frame conditions may differ | Treat no-drill replacement as a conditional conclusion |
| Assuming “SFIC” means any key will work | Key-system compatibility is separate from door fit | Verify core specification, keyway, pin count, and keying |
Frequently Asked Questions
How do I measure backset on a storefront door lock?
Measure from the door-edge or faceplate reference specified in the lock diagram to the lock’s operating centerline, often the center of the cylinder opening or spindle location. Keep the ruler perpendicular to the edge, show both endpoints in a square-on photo, record inches and millimeters, and verify the reference against the exact existing and candidate models.
Which backset sizes are available for EASILOK storefront locks?
Current EASILOK product information lists 31/32-inch, 1-1/8-inch, and 1-1/2-inch backset directions for relevant narrow-stile deadlock and deadlatch configurations. Confirm the exact model and current SKU. If an existing lock measures 7/8 inch, do not round or substitute 31/32 inch; the current SK1850 catalog does not list a 7/8-inch option.
Is door thickness the same as backset?
No. Door thickness runs across the structural door section from one face to the other. Backset runs from the specified door-edge or faceplate reference to the lock operating centerline. They are different measurements in different directions, and both must be checked together with the lock body, bolt or latch, holes, frame, and strike.
Can I install an EASILOK storefront lock myself, and when should I call a professional?
DIY may be reasonable only after the lock type, exact configuration, existing preparation, measurements, frame, and receiver are confirmed and the current instructions are understood. Call a qualified professional for unidentified or modified preparations, misaligned or damaged doors, SFIC key-system work, life-safety questions, glass-door handling, restricted bottom-rail access, or any work beyond your experience.
Sources and Verification
- Adams Rite MS1850S Series Deadlocks
- Adams Rite 4510 Standard Duty Deadlatch
- CRL 777S Door Rail Floor Lock
- EASILOK storefront deadlock collection
- EASILOK storefront deadlatch collection
- EASILOK bottom-rail lock collection
The EASILOK backset and door-thickness directions were checked against the current EASILOK catalog and product documentation. Measurements must still be verified against the exact product configuration and field conditions. Last reviewed: July 28, 2026.
Measure First, Then Verify the Candidate Model
First use the storefront lock identification guide to confirm the likely lock-body category. Then complete the measurement record and use the EASILOK SK1850 compatibility guide when evaluating an MS1850S-style deadlock. If any reference point, preparation, bottom-rail condition, or key-system requirement remains unclear, contact EASILOK support or a qualified door professional before ordering.