Planning an entry upgrade moves quickly once the vocabulary feels familiar. This guide explains each term in practical language and shows how the parts relate in a real project. Use it while you compare listings, verify sizes, and plan installation. Clear terms keep door buying efficient and reduce returns by helping you order exactly what you need among the many door components on the market.
Understanding Door Types
The door type you choose determines what arrives at your home and how the installation will go. Listings that look similar can include very different parts, so slow down and match the package to your project. Use this mini door buying guide to align scope, tools, and delivery limits before you click purchase.
Slab (a.k.a. Door Slab)
Only the door panel. No frame, hinges, threshold, or trim. Choose a slab when your current frame is plumb and solid, or when you already have new frames readily available. You will always need a set of door frames that go with the door slab when building an entrance.
Knock-down Door Kit (Door Kit)
A complete set shipped in a compact package, ready to be assembled on site. It comes with the door slab, door frames, and every other accessories required to build an entry system. It balances cost, space, and a clean finish with standard homeowner tools.You can reference a example like FRAMEWELL 36 X 80 Inches 8 Lite Fiberglass Entry Knock-down Door Inswing Hand to visualize the parts included and the assembled look without committing to a specific style.
Pre-Hung Door
A factory-assembled frame with the slab hinged and aligned, with no on-site assembly required. Best for new construction or when you want to replace your entire entry system in the most convenient way. A pre-hung unit is bulky and rigid, so plan the delivery path and clear landings in advance. The unit is rigid, so measure hall turns and doorways to avoid surprises on installation day.
Door Components & Terminology
Shared vocabulary makes product pages readable and quotes comparable. When you and your installer name the same door components, ordering the right items becomes easy, trim fits on the first try, and the finished seal performs as designed. The terms below appear on nearly every spec sheet in door buying.
Jamb
The two vertical sides and the head that create the opening carry hinges and the latch. If you have ever typed “what is a door jamb,” picture the structural frame inside the trim. Order the correct jamb depth so the casing sits flush with the wall. Common depths are 4-9/16 inches for 2×4 walls and 6-9/16 inches for 2×6 walls with 1/2-inch drywall. Confirm kerf grooves if you plan to use kerf-in weatherstripping as part of your door components list.
Door Frame
The full frame assembly that surrounds the slab, including both jambs, the head, and the sill area. When listings say “includes frame,” they mean this complete structure. A square, well-built frame makes latching smooth and keeps weather seals compressed evenly along all edges.
Casing
Interior trim that bridges the wall and frame, hiding shims and insulation. Casing style sets the mood: simple square edge for modern rooms, stepped or beaded profiles for traditional spaces. Primed or prefinished options reduce paint time after install and keep lines crisp at the corners.
Threshold / Sill
The horizontal structure at the bottom that connects the exterior landing to the interior flooring. Adjustable sills let you raise or lower the contact point for a tight seal after the seasons change. Use the credit-card test: close the door on a card under the sweep; a light drag means a good seal without scuffing floors. Recheck after rugs or new flooring are installed.
Essential Door Measurements
Size mistakes cause the most returns, not bad products. Measure in the right order, label numbers clearly, and take photos of the opening. If you want a visual refresher, look up “how to measure rough opening.” Understanding “door unit size vs door size” prevents cart errors and keeps the delivery day calm during door buying.
Rough Opening (RO)
The framed hole in the wall that accepts the full door unit. The RO is slightly larger than the unit, so you can shim it square and insulate the gap. Check for level at the sill and plumb on both sides, since a tilted RO forces the slab to rub or the latch to miss.
Door Size
The dimensions of the door slab only, no frame, jambs, threshold, or trim. Use Door Size when you will keep the existing frame. Measure the slab’s width and height to the nearest 1/8" (use the smallest width measured across top, middle, and bottom), note the slab thickness, and confirm the hinge side and lock bore pattern so the new slab aligns with the existing hinges and hardware.
Unit Size
The outside-to-outside dimensions of a complete prehung unit, including jambs and threshold, with the slab installed. Unit Size must fit through your path of travel and into the wall opening. Plan for the rough opening to be about 1/2"–3/4" larger than the Unit Size in width and height to allow shimming and insulation; this space ensures the unit can be set plumb, latch smoothly, and seal correctly.
Quick reference example
| You’re measuring | Relevant Dimensions | Why it matters |
| Existing slab inside a good frame | Door size | Confirms you only need a new door slab and can keep the existing frame and trim in place. |
| Framed wall opening | Rough opening | Confirms the prehung unit will fit the rough opening with enough space for shims so it can be set plumb and sealed. |
| New assembled frame | Unit size | Verifies the prehung unit can pass through hallways and doorways and into the opening without binding. |
Understanding Door Handing
Handing affects the hinge side and swing direction. Furniture placement and weather exposure are common factors to consider when deciding what's the right Door Handing for you.
Handing
Stand outside the home. If hinges are on your left, it is left-hand; on your right, right-hand. Add swing next: inswing or outswing. Many charts use Left-Hand Inswing (LHI), Left-Hand Outswing (LHO), Right-Hand Inswing (RHI), and Right-Hand Outswing (RHO) to combine hand and swing. Make sure the door components (hinges, latches) match the handing of your door.
Inswing
The slab opens toward the interior, outswing is less common for a residential entrance. It protects hinges and helps the bottom sweep stay out of heavy rain. Before ordering, tape your floor plan and swing arc to verify clearance for console tables, coat hooks, and stair newel posts.
Outswing
The slab opens toward the exterior. It frees interior space and resists wind pressure when latched well. Check that exterior sconces, mail slots, and house numbers do not block the swing, and consider security hinges with non-removable pins.
Door Materials
Material picks set maintenance, energy performance, and impact resistance. Think about sun, rain, and local salt air, then balance the look against upkeep. If durability and efficiency rank high, read about “fiberglass front door advantages” while you compare samples during door buying.
Wood
A rich, warm look with a wide range of profiles. It rewards regular finish care. In high sun or wet conditions, plan a maintenance schedule and choose a finish system rated for exterior use so joints stay tight and color holds.
Fiberglass
A tough skin with low upkeep and often a foam core for insulation. There are plenty of woodgrain options available if you want the aesthetics of a wood door. Daily bumps from bags and gear leave fewer marks, which suits busy households and rentals where traffic is high. For added durability and curb appeal, fiberglass entry doors offer these benefits while maintaining the look you want.
Steel
A secure, budget-friendly shell that feels solid. Watch for corrosion near sprinklers, coastal air, or concrete pads that hold moisture. Follow paint and sealant schedules and keep the bottom edge well sealed so the skin stays protected.
Styles & Glass Options
Style sets curb appeal, and glass manages daylight and privacy. Decide how much light you want at eye level versus above the door. Opacity and texture matter as much as size. Use consistent labels across listings for faster filtering in door buying.
Flush Door
A flat surface that pairs with square trim and clean hardware. Good for modern elevations and minimalist interiors. The smooth skin makes cleaning quick and shows paint colors crisply without visible grain.
Panel Door
Recessed or raised panels form shadow lines and a classic profile. Common examples include a six-panel colonial for traditional homes, a three-panel shaker for clean lines, and a two-panel arch top for a softer look. Match panel count to the facade: more panels read formal, fewer panels feel modern. When comparing door components, check panel depth and rail width so profiles align with your interior trim.
Lite
Any glass pane inside the slab. Layouts are labeled 2-Lite, 3-Lite, 6-Lite, and similar. Choose opacity to balance privacy and light: frosted or rain glass are high-privacy options, while styles with clear glass up high and solid panels in the center brighten the foyer without exposing the interior.
Sidelite
A tall glass panel beside the slab, single or double. Great for brightening your entry with additional daylight, especially for door slabs that don't have lites. Use tempered or laminated glass for safety and consider textured patterns where the entry sits close to the sidewalk for privacy.
Transom
A horizontal window above the slab that adds daylight without exposing the room at eye level. Transom is an elegant addition that adds sophistication and height to your entrance. Keep the head trim proportionate to the size of the door slab for an aesthetically balanced look.
Grille
Decorative bars that divide a glass area into smaller visual panes (divided lites). Four common constructions are used: simulated divided lites with grilles between glass (SDL with GBG), where raised bars are applied to the exterior and interior faces of the glass and aligned with a matching grille sealed between the panes, creating a deeper traditional look while keeping both sides smooth for easy cleaning; simulated divided lites (SDL), where bars are bonded to one or both faces of the glass to mimic true divided panes, sometimes with an internal spacer for extra depth; grilles between glass (GBG), where bars sit inside the insulated glass unit so both sides of the glass are smooth and simple to clean, with a flatter appearance; and fixed grilles, which are non-removable bars integrated into the sash or lite frame to create a permanent pattern with durable alignment.
Additional Hardware & Features
Hardware defines the feel and weather performance every time the door moves. Hinges, strikes and seals are accessories that ensure the entry system works as one.
Hinges
Pivot hardware that carries the slab and sets the swing feel. Most 1-3/4-inch entry slabs use three 4-inch hinges. Tall or wide units often add a fourth for support.
Strike Plate
The metal plate on the frame where the latch engages. Upgrading to a long strike with 3-inch screws ties the plate into the wall framing for a firmer close. Accurate alignment prevents rattles and helps compress weather seals evenly.
Weatherstripping
Compressible seals around the frame plus a bottom sweep that blocks drafts and water. Compare weatherstripping types to match your climate, for example, bulb seals for consistent compression or magnetic seals for a crisp close on steel skins.
Put These Door Buying Terms To Work
Good door buying comes from clear terms, clean measurements, and a plan that fits your home. Pick the type that matches your situation, write down door size, unit size, and rough opening, then mark handing from the exterior. Choose materials and glass that fit the climate, privacy, and daily traffic. Keep this glossary nearby while you review door components, and move from checkout to a smooth first close with confidence.
Frequently Asked Questions
Q1. Do I need a permit for an entry door replacement?
Many cities allow like-for-like replacements without a permit if the size and location stay the same. Enlarging openings, moving the door, or altering the structure usually triggers permits and inspections. Check your local building department and any HOA approval rules before ordering.
Q2. Which energy ratings matter on glazed entry doors?
Look for the NFRC label. Lower U-factor means better insulation. SHGC should match your climate: lower in hot, sunny regions; higher in cold regions seeking passive solar gain. If available, pick units meeting your state’s ENERGY STAR climate zone requirements.
Q3. How do I keep water out at the threshold?
Install a sill pan, preformed or site-built with self-adhered flashing, sloped to the exterior. Bed the threshold in sealant, flash jambs, and foam the sides with low-expansion insulation. Leave drainage paths clear and re-seal fasteners exposed to weather.
Q4. What clearances support egress and accessibility?
For residential main egress, many jurisdictions target a 32-inch minimum clear opening when the door is open 90 degrees. ADA guidance limits thresholds to 1/2 inch maximum with bevels. Local code governs details, so verify requirements before you finalize sizes and swing.
Q5. Will my smart lock fit a new slab?
In most cases, yes. Check your smart lock's installation guide for specific requirements for bore dimensions and spacing. Typical dimensions to look out for are, a 2 1/8 inch face bore, a 1-inch edge bore, either a backset of 2 3/8 or 2 3/4 inches, and an overall door thickness of 1 3/4 inches. Some smart lock kits such as Mortise, Multipoint, Euro Cylinders, or extra-thick doors, may need special prep, adapter kits, or professional installation.
