How do I patch a hole in drywall so it actually disappears?
Anyone can fill a hole in drywall. The difference between a repair that vanishes and one that announces itself every time the afternoon light rakes across the wall is almost entirely in the finishing — the taping, mudding, and sanding that happens after the hole is filled.
Match the fix to the hole
Dents and nail pops need nothing more than a skim of joint compound ("mud"), a light sand once dry, and a second thin coat. For a nail pop, drive a drywall screw an inch or two above and below the popped fastener first so the panel is held tight to the stud, then fill.
Small holes — doorknob strikes, anchor holes up to a few inches — are the territory of the adhesive mesh patch or the "California patch," where you cut a slightly oversized square of drywall, snap the gypsum off the edges, and leave a paper flange that takes the place of tape. Either way, the patch itself is the fast part.
Larger holes need backing. Cut the ragged hole into a clean rectangle, screw furring strips or scrap lumber inside the opening so they bridge it, then screw a same-thickness piece of drywall to the backing. Drywall commonly comes in 1/2-inch and 5/8-inch thicknesses; matching it matters, because a patch that sits proud or shallow can't be hidden with mud.
The finishing is the repair
Every seam around a patch gets tape — paper or mesh — embedded in compound, then two or three progressively wider coats, each feathered farther out than the last. The goal is a hump so gradual the eye can't find it: a patch mudded eight or twelve inches wide disappears; the same patch mudded three inches wide becomes a permanent bump. Between coats, let the mud dry fully and knock down ridges. Sand the final coat with fine grit, prime the patch (bare compound drinks paint differently than the surrounding wall), and then paint.
If you want to do this the way the trade does, the industry's code-referenced standard for hanging and finishing gypsum panels is GA-216, Application and Finishing of Gypsum Panel Products, published by the Gypsum Association. It covers fastening, joint treatment, and application details, and it's the document building codes point to when they say drywall shall be installed "per the standard." You don't need to buy it to patch a hole, but it's useful to know that an authoritative answer exists when a contractor and an inspector disagree.
One caution in older homes
If your home was built before 1978, the paint on and around the damaged area may contain lead, and sanding is exactly the activity that turns intact paint into dust. Federal rules under the EPA's Renovation, Repair and Painting (RRP) Program require firms doing renovation work that disturbs paint in pre-1978 homes to be certified and to follow lead-safe work practices. If you're hiring the work out on an older house, ask whether the firm is RRP-certified before you ask about price — see our guide to painted walls in pre-1978 homes for what the rule does and doesn't cover.
When to call someone
A patch is DIY territory. Call a pro when the hole is the symptom rather than the problem — recurring cracks along the same line, a soft or damp patch (see why is my wall damp?), or damage near plumbing or electrical. And before you commit either way, run the numbers through the cost estimator so you know what "normal" looks like for your scope.