What Size Door Knob Do I Need? Backset, Bore Hole and Thickness
Most US homes need a door knob that fits a 2-1/8 inch bore hole with a 2-3/8 or 2-3/4 inch backset, on a door 1-3/8 to 1-3/4 inches thick. Measure those three things before you buy, and the right knob or handle is easy to pick. Many modern sets have an adjustable latch that covers both common backsets.
Kwikset 96900-463Best overall
Estmoon Most keys included
Gobrico 12061-01Lightest in the lineupThe three measurements that decide fit
"Door knob size" really means three numbers: the backset, the bore hole diameter and the door thickness. A knob that matches all three will install without drilling or patching.
The same numbers apply to door handles (levers). A lever and a knob use the same hole and latch, so the sizing steps below work for both.
- Backset: the distance from the edge of the door to the center of the large bore hole. Most residential doors use 2-3/8 inches or 2-3/4 inches.
- Bore hole: the large hole drilled through the face of the door. A common size is 2-1/8 inches (54 mm).
- Door thickness: the distance between the two faces of the door. Standard residential doors are often 1-3/8 or 1-3/4 inches thick.
How to measure your door
You only need a tape measure. If you are replacing an existing knob, you can measure the empty hole once the old hardware is off. If the door is new or has never been drilled, you will measure the planned position instead.
Take each measurement twice. A small error in backset is the most common reason a new latch will not reach the center of the hole.
- Open the door and measure from the edge to the center of the large hole. That is your backset. If it is close to 2-3/8 inches, treat it as 2-3/8. If it is close to 2-3/4 inches, treat it as 2-3/4.
- Measure across the large hole to get the bore diameter.
- Measure the thickness of the door at the edge.
- Check the small hole in the door edge. This is where the latch sits, and it should line up with the large hole.
Standard sizes at a glance
The table below shows the most common residential sizes and what to look for on the package. The ranges in the last row come from the sets on our spec sheets.
Our best door hardware page lists several sets that fit this range, so you can compare them once you know your numbers.
| Measurement | Common residential size | What to check |
|---|---|---|
| Backset | 2-3/8 in or 2-3/4 in | Match your door, or pick an adjustable latch |
| Bore hole | 2-1/8 in (54 mm) | Confirm the set's stated hole size |
| Door thickness | 1-3/8 in to 1-3/4 in | Check the minimum and maximum on the box |
| Ranked sets on our page | 1.375 to 1.75 in thick, 2.375 or 2.75 in backset | Fits most standard doors |
Choose the right function, not just the size
Size is only half of the decision. The knob also has to do the right job for the door.
A passage set never locks, so it suits hallways and closets. A privacy set locks from the inside with a thumb turn, which suits bedrooms and bathrooms. An entry set locks with a key outside and usually pairs with a deadbolt.
Entry doors often have two holes: a large one for the knob and a smaller one for the deadbolt. Check that your door has both before you buy a combo set. Our best door hardware page explains how security grade and cycle ratings help you judge entry sets.
What size knob for a wardrobe or cabinet door?
Wardrobe and cabinet doors are a different case. They rarely use a bored latch set like a room door. Most use a small knob or pull held by one or two screws.
For those, measure the existing screw hole spacing, then match the new knob to it. Many knobs use a single screw, so there is no spacing to match. For pulls with two screws, measure from the center of one screw hole to the center of the other.
A full-length wardrobe door that swings like a room door may take a standard latch set. In that case, use the same backset, bore and thickness steps above.
Safety and installation notes
Installing a knob is a simple job, but a few precautions help. Wear safety glasses when drilling or chiseling, because wood chips can fly. If you need to drill a new bore hole, use a hole saw with a drill that you can hold firmly with both hands.
Do not drill into a door without checking that there are no wires or pipes inside a wall next to the frame. If the door is old, test a small area of paint first, since older finishes may contain lead. Wear a dust mask when sanding.
Keep fingers clear of the latch while testing, and use a stable step stool for any door higher than you can comfortably reach.
If your measurements do not match
If your backset is neither 2-3/8 nor 2-3/4 inches, or your door is thicker or thinner than standard, a standard set may not fit. Older and custom doors can fall outside the usual ranges.
In that case, look for a set that lists your exact dimensions, or ask a hardware store about a thicker door kit or a different latch. A larger hole can sometimes be covered with a wider rosette, but a hole that is too small needs careful enlarging with the right hole saw.
Frequently asked questions
Can I use a knob on a door that has a lever now?
Yes, in most cases. Knobs and levers share the same bore hole and latch sizes, so you can swap one for the other if the measurements match.
Does the door's left or right swing matter?
For many sets it does not, because the handing is reversible. Check the package, since some knobs and levers are made for one side only.
What if the old hole looks bigger than the new knob?
Look at the rosette, the round plate behind the knob. A wider rosette can cover a larger hole, but a hole that is too small needs a careful enlargement.
Do I need a deadbolt hole for an interior door?
No. Interior doors usually take only a knob or lever, so the deadbolt hole matters mainly on entry doors.