Backset, Bore and Door Thickness: Measuring for New Door Hardware
Before you order new door hardware, take three quick measurements. They decide whether new levers or knobs will drop straight into the existing holes or need extra work. Each takes a tape measure and a minute.
1. Door thickness
Measure the edge of the door from face to face. In most US homes, interior doors are 1-3/8 inches thick and exterior doors are 1-3/4 inches thick. Most hardware fits both, but thicker doors (2 inches and up, common on custom and solid wood doors) often need a thick-door kit with longer spindles and screws. Check before you order.
2. Backset
The backset is the distance from the edge of the door to the center of the large hole for the handle. The two US standards are 2-3/8 inches, the most common on interior doors, and 2-3/4 inches, common on exterior doors and on doors with wide stiles. Many latches are adjustable between the two, but some decorative sets are made for one only. Narrow-stile doors such as glass and aluminum doors use much shorter backsets and need special hardware.
3. Bore sizes
The large hole through the face of the door is the cross bore. The US standard is 2-1/8 inches in diameter. The smaller hole in the edge of the door, where the latch sits, is the edge bore, usually 1 inch. If your door has these standard holes, most modern US-market levers and knobs will fit. Many European and designer brands use different spacing, a rectangular mortise lock or a smaller bore, so read the specifications closely.
Tubular latch or mortise lock?
Most American interior doors use a tubular latch: a small cylinder in the edge bore. Older houses and many high-end doors use a mortise lock, a rectangular box set into a deep pocket in the door edge, with a separate keyhole and spindle. Mortise hardware and tubular hardware are not interchangeable. If you see a tall rectangular faceplate on the door edge, you have a mortise lock, and you will need mortise-compatible trim or a new door prep.
Rose, backplate and coverage
If you are replacing old hardware, look at the marks and paint lines it leaves. A small round rose may not cover the outline of a large old backplate. Choosing a long backplate, or planning for paint touch-up, avoids a visible ghost of the old hardware.
A simple checklist
- Door thickness, face to face.
- Backset, door edge to center of the cross bore.
- Cross bore diameter and edge bore diameter.
- Tubular latch or mortise lock.
- Handing, if the hardware is a lever or is shaped (see our handing guide).
Recommendations in our guides may link to retailers. See our affiliate disclosure.