For the wider project, the windows and doors guide<\/a> covers how interior and exterior doors fit together, and window and door installation cost<\/a> handles the budget side.<\/p>\n Before any tools come out, the single most useful decision is which installation you are actually doing. They look similar and they are not interchangeable.<\/p>\n You are installing a prehung unit<\/strong> when the frame arrives with the door already hanging in it. The unit drops into the rough opening as one piece and you shim, square, and fasten it. This is the most common job in new construction and in remodeling where the frame is being replaced.<\/p>\n You are hanging a slab<\/strong> when the existing frame stays and only the panel is replaced. This is the most common job in a house being updated room by room, because the framing is already there and the frame is usually fine.<\/p>\n You are deciding what to buy<\/strong> when nothing is ordered yet. The choice determines who does the squaring work, and it is a bigger decision than it looks.<\/p>\n The distinction matters because a prehung unit absorbs small errors. Its frame is already squared by the manufacturer, so shimming absorbs what little mismatch there is. A slab has no such forgiveness. Every assumption about the frame, the hinges, and the hardware becomes visible the moment you hang it.<\/p>\n So: how to install a prehung interior door<\/a> is the sequence for a new frame, how to install an interior door slab<\/a> is the sequence for a panel swap, and how to measure an interior door<\/a> comes first either way, because the numbers you order against decide whether the door fits at all.<\/p>\n Before you order anything, decide whether the frame survives the job: how to replace an interior door slab without replacing the frame<\/a> covers the inspection that settles it.<\/p>\n Doors are mechanical devices. They are a slab held in a frame by hinges, with a latch that has to meet a strike plate<\/a> within a fraction of an inch. Every tolerance on this page exists because of how that system moves.<\/p>\n A gap of 1\/8 inch at the hinge side causes binding. A gap of 3\/16 inch at the latch side causes drafts and noise. A drop of 1\/4 inch at the bottom causes scraping on carpet or dragging on hard floors.<\/p>\n The working tolerances<\/a> are: hinge side gap 1\/8 inch, latch side gap 1\/8 inch, bottom gap 3\/4 inch above the finish floor, and plumb within 1\/8 inch over 8 feet. Anything outside these requires shimming or trimming, and the order you do that in matters more than most people expect.<\/p>\n There is one rule that separates a door that works from a door that never quite does: shim first, check second, fasten last.<\/strong> A jamb nailed tight against a stud that is not perfectly plumb does not become plumb. It bows, and the bow is the reason a door binds in June and closes fine in January. When a door that is already hung will not close or latch, the fix is a diagnosis, not a reinstall, and how to fix an interior door that won’t close<\/a> walks through it.<\/p>\n Most wrong-door orders trace back to one confusion, so it is worth being precise about it. A door project contains three different measurements, and they are commonly all called “door size.”<\/p>\n The slab size<\/strong> is the panel. The unit size<\/strong> is the slab with its jambs attached. The rough opening<\/strong> is the hole in the wall. Each is bigger than the last.<\/p>\n That is why the rough opening rules seem to contradict each other. Home Depot’s prehung instructions say the opening must be 2 inches wider than the door. The Lowe’s Masonite sheet says 1\/2 inch wider than the unit. Both are correct, because one measures from the slab and the other from the unit, which already includes the jambs.<\/p>\n The practical rule: measure the smallest of three readings in both directions, identify which of the three numbers you actually measured, and then work from your own manufacturer’s sizing chart. The measuring guide<\/a> has the full table and the decision tree.<\/p>\n From the manufacturer instruction sheets, the core kit is modest: a level of at least 24 inches, a 24-inch framing square, a hammer and nail set, wooden shims, 8d and 16d finish nails, a Phillips screwdriver, putty knife and wood filler, and a fine-toothed saw or jig for trimming. Add safety glasses, and a dust mask if you are cutting MDF or composite stock.<\/p>\n Budget for shims more than you expect. They are cheap, they are the mechanism that lets you correct an irregular opening without cutting anything, and a single door can eat a surprising number of them.<\/p>\nFirst, Work Out Which of the Three Jobs You Have<\/h2>\n
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Why Precision Matters More Than Effort<\/h2>\n
The Three Measurements That Decide Everything<\/h2>\n
Tools, Materials, and What a Job Costs<\/h2>\n