Door Lock Backset: How to Measure 2-3/8″ vs 2-3/4″ (60/70 mm)

Measure backset from door edge to bore center: 60 mm (2-3/8 in) vs 70 mm (2-3/4 in), EU 55/60 mm options, and mistakes that misalign hardware.

Last updated: November 2, 2026

Installation & Hardware · Last updated: 2 November 2026 · Jusen Doors Technical Team · Reviewed by Jusen Doors Engineering Team

Door Lock Backset: How to Measure 2-3/8″ vs 2-3/4″ (60/70 mm)

Quick answer: Backset is the horizontal distance from the door edge to the centre of the spindle or key/cylinder bore. In North America the common bored-lock backsets are 2-3/8 in (about 60 mm) and 2-3/4 in (about 70 mm). Many metric mortise locks use different case and backset dimensions, often around 50-60 mm, so measure the existing preparation and state the lock model rather than copying a nominal size. A 1-3/8 in figure usually describes door thickness, not backset.

Measure from edge to bore centre

Open the door and measure from the finished lock edge to the centre of the round cross-bore or spindle. For a mortise preparation, measure from the door edge to the spindle/cylinder centreline shown on the lock template. Use a caliper or steel rule and record both millimetres and inches as measured; do not convert then round twice. Photograph the tape in place when sending dimensions to an overseas factory—one image prevents most datum arguments.

Choose 60 mm or 70 mm for the right reason

The shorter North American backset keeps the knob or lever closer to the edge and is common on residential interior sets. The 70 mm option moves the grip farther from the frame and is often used where knuckle clearance, larger roses or particular lock functions demand it. Narrow stiles, glazed doors and aluminium profiles may restrict the lock case more than the nominal backset. Check stile width, glass position and door thickness before selecting hardware.

Do not confuse the four lock dimensions

Backset is horizontal position. Centre distance is the vertical spacing between spindle and cylinder on a mortise lock. Case depth determines how far the lock body sits into the leaf, and door thickness determines spindle and screw length. Replacing one number with another produces misaligned cylinders and handles. Factory machining drawings should list all four, plus hand, function and the finished-floor height of the spindle.

Retrofit checks before ordering handles

Measure the existing backset, bore diameter, edge preparation, door thickness and distance from the bore to any panel moulding or glass. Adjustable latches can solve a 60/70 mm bored-lock mismatch in some products, but they do not convert a mortise preparation to a tubular one. On fire doors, new machining outside the listing can be prohibited; match the listed lock preparation rather than enlarging holes on site.

Write the factory instruction once

A clean purchase instruction reads like: lock model and function; backset in millimetres from finished edge to spindle centre; spindle height from finished floor; cylinder centre where applicable; door thickness; hand; and sample door to be measured before batch drilling. Pair it with the mortise vs cylindrical comparison when the lock family itself is still undecided.

Specification checklist: what to confirm before ordering

Finished-floor datum, structural opening and frame dimensions measured before machining.
Leaf size, thickness, hand, swing and clearance targets frozen on the door schedule.
Hinge template, handle height, backset and lock/hole positions stated from the same datum.
One approved reference opening checked before repetitive installation.
Cut edges sealed and rated-door machining kept inside the approved scope.

Related guides

Ordering factory-machined doors?
Send the door schedule, finished-floor datum and hardware templates so hinge and lock preparations can be checked before production.
Request a specification check · Browse the guide hub

FAQs

Is 1-3/8 inch a backset size?

In ordinary door terminology 1-3/8 in (35 mm) most often refers to interior door thickness. Common North American bored-lock backsets are 2-3/8 in and 2-3/4 in.

Can I change from 60 mm to 70 mm backset?

Sometimes with an adjustable latch or a new preparation, but the handle position, existing bore and door stile must allow it. On rated doors, stay inside the permitted machining scope.

Where exactly is backset measured?

From the finished door edge to the centreline of the spindle/bore, not to the edge of the hole or the outside of the rosette.

Data note: Figures described as typical, common or planning ranges are industry budgeting ranges with the stated assumptions. Building-code duties, tested scope and final quotations depend on destination, selected construction and order schedule.