Backplate Size for Old Holes: Do the Math, Then Cover the Ghost

The backplate size for old holes is arithmetic, not taste. Take the old center-to-center spacing, add the diameter of one hole, then add at least 1/4 in of plate beyond the outer edge of each hole. A 3 in pull swapped for a knob therefore needs a plate at least 3-11/16 in long. One thing overrides that number: the outline the old hardware left on the door. If the finish under the old pull's feet looks different from the finish around it, the plate has to hide that shape, and that shape is usually bigger than the holes.

Three measurements to take before you shop

The spacing. Measure from the center of one old hole to the center of the other, or, easier, from the left edge of one to the left edge of the next; equal holes give the same number. I write it down in millimeters as well as inches, because many pulls are sold on metric spacing, and 3 in (76 mm) and 96 mm sit close enough to confuse anyone reading a tape at arm's length.

The hole itself. Push drill bits into the hole shank first, working up a size at a time, until one fits snug without forcing. That bit is your hole diameter. Holes for the standard 8-32 hardware screw are commonly drilled at 3/16 in, but a hole that held a loose pull for a decade has usually been worked oval. Measure an oval hole across its longest direction, and take your margin from there.

The footprint. Take the old hardware off and look along the door in daylight, with your eye almost level with the surface. Wood that sat in light for years has changed color everywhere except under the feet of the old pull. Painted doors show a cleaner, brighter patch where the hardware sat, and drawers that get opened all day carry a dull halo where fingers landed. Outline whatever you see with painter's tape. I size the plate to the tape, not the holes; the holes are only the part of it a ruler can find.

The sizing rule, worked out

Minimum plate length equals the old spacing, plus one hole diameter, plus two margins. Minimum plate width equals one hole diameter plus two margins, or the width of your taped outline, whichever is larger. I treat 1/4 in as the floor for that margin and go to 3/8 in when the holes are torn or the door carries a visible ghost. Window light rakes across a door at a low angle, and a hole edge sitting right at the plate's edge is the first thing it finds.

Two cautions on reading a listing. The overall length and width of a plate are one set of numbers; the holes drilled through it are another. A pull backplate sold for 96 mm hardware tells you the hole spacing in its name and the plate size somewhere further down, and you need both. And a plate described as a knob backplate is often sized for a knob alone, a small oval or square that will not reach across two old holes. If your old hardware was a pull, check the length before you check the style.

Pull to knob: the old pull chooses where the knob sits

The detail almost nobody mentions here is placement. A knob plate is drilled through its middle, so to cover both old holes evenly, the knob has to land at the exact midpoint between them. You drill one new hole there and the plate hides the rest. The old pull has quietly decided where your new knob goes.

On a drawer that costs nothing, because a knob belongs at the horizontal center anyway. On a door it moves the knob away from the corner by half the old spacing. Knobs normally sit 2-1/2 to 3 in from the corner, on the stile opposite the hinge. Behind an old 3 in pull mounted vertically, the knob ends up 1-1/2 in further along the stile, which very few people would ever spot. Behind an old 5 in pull it moves 2-1/2 in, the plate has to be close to 6 in long, and a small round knob centered on a long strip of metal stops looking like a knob with a plate and starts looking like a repair. That is the point where I would fill the holes rather than cover them.

One installation habit matters here. A knob plate is clamped by a single screw, so a plate that is not seated firmly can swing out of square the first time somebody twists the knob. Some plates carry small prongs on the back that bite into the door; flat ones depend on the screw alone. Snug the screw with the plate held square, then check it again after a week of use.

Pull to pull: a plate drilled for the new spacing that still reaches the old

Pull backplates come pre-drilled for one spacing, so the plate has to match the new pull while also covering the old holes. Which way you are moving decides the trouble.

Going longer, say from 3 in to 96 mm, puts the old holes inside the new ones, and any plate that fits the new pull covers them. The hazard is a near miss. Each new 96 mm hole lands about 3/8 in (10 mm) outside an old 3 in hole, enough to leave solid wood between them. Spacings closer than that, such as 96 mm against 4 in, put the new hole partly inside the old one. The bit drifts into the empty side, the hole wanders, and the pull goes on crooked. The fix I would use is to plug the old holes with glued dowel or a hardwood filler first and drill through the plug. Under a backplate the plug never has to look good; it only has to hold the bit straight.

Going shorter, from 5 in down to 96 mm, leaves the old holes outside the new pull's feet, and the plate has to reach them: by the table, at least 5-11/16 in long, drilled at 96 mm.

Same spacing needs no plate at all unless the footprint shows. One near-match is worth knowing: 5 in and 128 mm differ by about a millimeter, which an old hole eased very slightly with the same bit will usually absorb.

Knob to pull is the friendly direction. The single old hole sits on the new pull's centerline, halfway between its screws, and any plate drilled for the new pull covers it, provided the plate is wide enough for the footprint the knob left.

When filling the holes beats covering them

A backplate is a decorative object, and it carries period character, the look of older doors with more ornament on them. That is an advantage on a raised-panel or shaker door and a liability on a flat slab with a slim bar pull, where the plate reads as a patch. I would fill rather than cover in four situations: the doors are painted and getting repainted anyway, so filler disappears under the new coat; the door is a modern slab; the old pull was long enough that a knob plate turns into a strap; or the old holes sit somewhere the new hardware should not, such as one centered pull becoming two pulls on a wide drawer. The full filling method is in our guide to filling old hardware holes.

The reverse holds for stained wood, veneer, thermofoil and laminate. Filler cannot carry grain across a stained door, and thermofoil and laminate have no way to take a patch that will pass. On those doors I would choose the plate.

Matching the plate to the knob or pull

The match I trust is a plate from the same maker as the hardware, sold for that series. Several manufacturers design backplates as companions to particular knobs and pulls, so the finish, the edge profile and the proportions were settled before you arrived. Matching across brands is where it goes wrong, because the same finish name can describe two different colors from two makers, and the plate sits directly behind the hardware, the one spot where a small difference is impossible to miss. Order a sample first, and the cost is refunded with your full order. Hold the plate and the knob together under your kitchen lights before you buy a houseful.

A deliberate contrast is the other honest route: a dark plate behind a brass knob, for instance, where the difference is too large to read as a mistake. What fails is the near miss, two nickels or two bronzes a shade apart. Hardware has the same problem as holes in that respect. Clearly the same works, clearly different works, and almost the same is the one result the eye keeps catching.

Last, the screws. A plate adds its own thickness behind the hardware, while the screw packed in the box was sized for a bare door. Measure door plus plate, buy screws to that length, or use break-away screws snapped to fit.