Door Lock Bore & Backset Compatibility Check

Compare door thickness, backset and existing holes with the candidate’s official drawing.
Review measurement uncertainty, mismatches and installer checks, then save your report.

A model name alone cannot establish compatibility. Have the exact candidate drawing and door measurements ready. Results compare entered conditions and do not guarantee installation.

1. Candidate and drawing

Enter discrete positions as separate intervals. For a nominal dimension without a stated tolerance, enter it as both endpoints and confirm tolerance with the manufacturer.

2. Door structure, directions and scope

Use the manufacturer’s viewpoint for handing. Non-round geometry needs further review; a single diameter cannot describe it. Not required does not mean unmeasured.

3. Measurements and allowed dimensions

Measurement error differs from product tolerance. Enter measurement uncertainty as ± values and leave unknown values blank.

Door thickness (mm)

Allowed interval 1

Backset (mm)

Allowed interval 1

Measure from the door edge to the cross-bore center. Two positions such as 60 OR 70 are not a continuous 60–70 range.

Round cross-bore diameter (mm)

Select round to compare diameter. Other or unknown geometry requires review.

Specified center spacing (mm)

Allowed interval 1

4. Site flags and drawing confirmation

Editing an input clears drawing confirmation. Unselected site flags are not independently verified.

Review results

Pending drawing confirmation

All results use mm. Center-value differences are not machining amounts. Boundary status can occur with zero center difference when uncertainty crosses a limit.

Door thickness

Unconfirmed

Measured interval: ?

Entered limits: ?

Center difference: —

Backset

Unconfirmed

Measured interval: ?

Entered limits: ?

Center difference: —

Round cross-bore diameter

Unconfirmed

Measured interval: ?

Entered limits: ?

Center difference: —

Specified center spacing

Unconfirmed

Measured interval: ?

Entered limits: ?

Center difference: —

  • Door/frame material: Unconfirmed
  • Handing: Unconfirmed
  • Swing: Unconfirmed
  • Complete hole pattern: Unconfirmed
  • Fire door / damage / modification flags: Unconfirmed

Review with the installer

  • Exact model, market, drawing revision and handing viewpoint
  • Edge latch, mortise pocket, screw positions and complete hole pattern
  • Clearance on both sides, handle/frame/gate interference and old marks
  • Reinforcement, damage, fire-door conditions, alteration approval and extra quote

Check replacement lock dimensions before ordering

A replacement may have the features you want yet require different holes or mounting hardware.
Matching door thickness alone does not establish that the backset, cross-bore or screw positions match.
Discovering these differences after delivery can create return and additional installation costs.

This calculator compares your existing door measurements with the official installation drawing for the exact candidate model.
It reviews thickness, backset, round cross-bore diameter and a specified pair of hole centers, including measurement uncertainty.
Material, handing and swing direction remain separate checks.
No product database or universal national lock dimensions are assumed.

Your next action

Save the TXT review and check it before sharing it with an installer.
Include the model, drawing revision, photos of both faces and the edge, old marks and any anticipated alterations.
The calculator does not send the report or place an order; inputs are used for this on-screen review.

Four dimensions and their reference points

Door thickness

Measure between the door faces where the lock is fitted.
Check whether decorative layers, steps or reinforcement plates are included in the manufacturer’s reference.
A thickness measured elsewhere on the door may not represent the actual fixing location.

Backset

This is the distance from the door edge to the cross-bore center.
Do not substitute a measurement from the frame, the handle tip or the lock body edge.
If existing hardware hides the center, obtain a drawing or installer measurement instead of guessing.

Round cross-bore diameter

This describes the round opening through the door faces, not the edge latch bore.
A distorted, slotted or rectangular opening cannot be represented by one diameter.
Selecting other geometry leaves this check unresolved and requires a full pattern review.

Specified center spacing

Use the distance between the same two centers identified on the drawing.
Edge-to-edge distances or a different pair of screw holes are not interchangeable.
Select not required only when the drawing confirms that this comparison is unnecessary; otherwise keep it unconfirmed.

Allowed dimensions and measurement error differ

Allowed endpoints come from the manufacturer for the specific model and accessory combination.
Measurement error describes uncertainty caused by the measuring tool, reference point or condition of the opening.
A larger error does not make the product more compatible: it widens the interval of possible door dimensions under review.

When only a nominal dimension is given

You can enter the same nominal value as both endpoints, then ask the manufacturer about permitted tolerance.
Nonzero uncertainty may produce a boundary result.
The calculator does not invent a construction allowance.
A blank value means unconfirmed, whereas zero error explicitly assumes no measurement uncertainty.

The input ceiling is a software validation limit, not a lock specification.
Dimensions must be positive; uncertainty must be nonnegative and no greater than the measured value; minimum must not exceed maximum.
Invalid values suppress results until corrected rather than leaving an old assessment visible.

Two backset positions are not a continuous range

A drawing may specify two discrete adjustment positions.
For example, 60 OR 70 does not imply that every value between them is supported.
Each dimension accepts up to two alternative intervals.
Only overlapping or touching intervals are merged for containment checks.

Fictional backset example

Suppose the allowed values are 59.5–60.5 mm OR 69.5–70.5 mm and the measurement is 65±0.2 mm.
Its interval is 64.8–65.2 mm, entirely in the gap.
The result is outside, and the center value is 4.5 mm above the first, nearest interval.
Entering one broad 59.5–70.5 mm range would incorrectly include that gap.
All these numbers are teaching assumptions, not a real model or a universal Korean specification.

Interval checks and dimension differences

Measurement interval and allowed set

With measured value x and error e, M = [x − e, x + e].
The allowed set is A = [a1, b1] ∪ [a2, b2], with the second interval optional.
Endpoints are inclusive and all comparisons use mm.

  • Within: all of M lies inside A.
    Only this entered dimensional condition has been met.
  • Boundary / remeasure: M intersects A but is not fully contained.
    Improve the measurement or confirm product tolerance.
  • Outside: M does not intersect any allowed interval.
    Review the candidate or discuss alternatives; machining feasibility is not calculated.
  • Unconfirmed: the model/drawing confirmation, required values or comparable geometry are missing.
    Missing information is never treated as a pass.

For the center value, the shortfall below an interval is a − x, the excess above it is x − b, and the difference inside it is zero.
For alternatives, the nearest interval supplies the displayed difference.
This is neither a required shift of the full uncertainty interval nor an instruction to remove material.

Worked example and endpoint cases

The fictional example uses a wooden door, left handing under the manufacturer’s viewpoint and inward swing.
Drawing confirmation starts unchecked so loading the example cannot immediately establish real compatibility.
Under the assumptions of matching material, directions and full pattern, with no site flags, confirmation changes the result to entered conditions met.

Fictional dimensions

  • Thickness: 45±0.5 mm / allowed 40–50 mm
  • Backset: 60±0.2 mm / allowed 59.5–60.5 OR 69.5–70.5 mm
  • Round bore: 54±0.2 mm / allowed 53.5–54.5 mm
  • Center spacing: 100±0.5 mm / allowed 99–101 mm

Change thickness only

At 40±0.5 mm, the 39.5–40.5 mm interval crosses the lower limit, producing boundary status.
At 40±0 mm, the exact lower endpoint is included, producing within status.
At 39±0.2 mm, the 38.8–39.2 mm interval has no overlap, producing outside with a 1 mm center shortfall.
A center difference of zero can therefore coexist with boundary status.

Material, handing, swing and the full hole pattern

Matching dimensions do not establish that hardware intended for wood supports a metal door and frame.
Select the existing material and confirm candidate support for the entire door/frame combination.
Handing and inward/outward swing are separate entries; select both only when that support is documented.

Use the drawing’s viewpoint

Left viewed from outside can differ from left viewed from inside.
Use the manufacturer’s stated viewpoint for both the existing door and the candidate.
A reversible handle alone does not prove that all swing directions, lock bodies and accessory combinations are supported.

A matching bore diameter and one spacing cannot describe every small hole or edge pocket.
Confirm the complete shape and pattern separately.
A known mismatch makes the overall result outside; an unconfirmed pattern requires further review.
Non-round pocket width, height and depth are not automatically checked here: show the full drawing to the installer.

From measurements to a saved review

  1. Record the exact model, sales market and official drawing name or revision.
    Check whether similar model names use different accessories.
  2. Enter measurements, uncertainty and documented allowed endpoints using matching reference points.
    Leave unknowns blank instead of estimating them.
  3. Select material, directions, geometry and whether spacing is required.
    Verify that you compared the same pair of centers.
  4. Flag fire-door conditions, damage, sag, reinforcement or alteration concerns.
    Confirm the drawing and inspect each result.
  5. Save the TXT review and resolve unknowns with the installer.
    Editing any input clears confirmation so changed conditions are reviewed again.

Switching between mm and inch converts existing values while preserving their physical dimensions.
1 inch = 25.4 mm, so 2.375 inch equals 60.325 mm.
When rounded dual-unit dimensions differ from exact conversion, confirm the manufacturer’s primary unit and tolerance instead of choosing the favorable value.
Comparison uses unrounded numbers even when the display shortens decimal places.

Practical uses and remaining site checks

Reusing existing preparation

Covering old marks is different from reusing fixing holes.
A matching main bore can coexist with different screw locations or an internal pocket mismatch.
If reinforcement is proposed, confirm plate thickness and compatible fixing hardware as part of the candidate configuration.

Online purchase and installation quotes

Request model-specific drawings rather than assuming a general compatibility statement defines universal dimensions.
Save a separate report for each candidate to avoid mixing specifications.
Use an installer’s actual quote for extra work; this tool does not calculate alteration or return costs.

Dimension matches do not approve installation

Review the strike, edge bore, mortise pocket, screws, body and handle clearances on both faces, and any secondary gate.
Fire-door conditions, damage, warping and permission to modify cannot be established from these dimensions.
Site flags keep otherwise matching inputs under further review; leaving a flag unchecked does not independently verify that condition.

Frequently asked questions

Can I enter only a product name without a drawing?

The model, drawing identifier and confirmation are all required before assessment.
There is no model lookup database, so do not invent missing specifications.

Can I order immediately if all dimensions are within limits?

The result compares entered conditions and is not an installation guarantee.
Resolve the full pattern, frame and edge details, accessories and site modifications with the installer before purchasing.

Are values between two backset positions allowed?

Unless continuous adjustment is documented, treat the positions as separate alternatives.
A measurement in the gap is outside both intervals.

Why is the result boundary when the difference is zero?

The center value can be inside while the measurement interval extends beyond a limit.
Check the reference point and measurement accuracy rather than hiding uncertainty by entering zero.

What if center spacing is unnecessary?

Select not required only when confirmed by the official drawing.
A measurement you have not taken must remain unconfirmed.

Does it check slots or mortise pockets?

Complex shapes and pocket depths are not automatically checked.
Other dimensions remain useful, but the overall review stays unresolved until the complete drawing is assessed on site.

Can foreign drawing dimensions be used for a Korean door?

Confirm that the drawing covers the exact model and sales market.
Foreign examples are not universal Korean specifications, and rounded inch/mm values may need manufacturer clarification.

What does the saved report contain?

It includes model and drawing information, original units and measurements, errors and limits, mm intervals, statuses and material, direction and site checks.
Unknowns remain visible for follow-up with the installer.

Manufacturer references and updates

Sources checked on 2026-09-21.
Schlage supports the dimension terminology and backset reference point; the model-specific igloohome guide illustrates separate material, clearance and hole-spacing checks.
Their model dimensions have not been installed as universal defaults.

Re-enter specifications when the manufacturer changes a drawing, accessory combination or market version.
This tool does not assess statutory certification, fire performance or installation permission, and does not explain bypass or forced entry.

Put measurements and drawings on the same basis

Start with the exact candidate and consistent reference points, then mark what remains unknown.
Outside results prompt candidate review; boundary and unconfirmed results prompt better measurements or manufacturer clarification.
Save the review and discuss site conditions to reduce missed questions during replacement.

Return to dimension review

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