Casing trim is the moulding that frames a door or window, covering the gap between the wall and the jamb for a clean, finished edge. It is one of the fastest ways to change how a room feels — the right casing profile can make a doorway look crisp and modern or warm and traditional. This guide walks you through casing styles, materials, sizes and installation, whether you are trimming a single doorway or finishing a whole home. Not sure where to start? Our design team can help you match casing to your doors, baseboards and overall style.
Casing trim is the flat or profiled moulding installed around the perimeter of a door or window opening. It sits over the joint where the jamb meets the drywall, hiding the shims and gap left during installation while giving the opening a defined edge. Casing works together with two other parts of the opening: the jamb (the frame the door or window sits in) and the doorstop (the strip the door closes against). For the full breakdown of how those pieces fit together, see our guide to the door jamb. Here, the focus is the casing itself — the visible trim that does most of the decorative work.
Door and window casing do not have to match, but in most homes they should. Using the same profile, width and finish on both keeps a room visually consistent, which is why matching casing is the default for new builds and renovations. The difference is mainly at the base: door casing runs down to the floor — often meeting a plinth block or the baseboard — while window casing usually returns around all four sides or sits on a stool and apron at the sill. If you are blending old and new trim, bring a sample of your existing casing to the store so we can match the profile as closely as possible.
Casing profiles fall into a few broad families, from simple flat boards to detailed traditional mouldings. Choosing a profile is mostly about the look you want and the era of your home.
Colonial casing is the classic, gently stepped profile found in many traditional and transitional homes. Its layered contours catch the light and add depth, making it a timeless choice that pairs naturally with Colonial baseboards.
Step bevel casing has a cleaner, more angular face than Colonial — a simple bevelled profile that reads as transitional. It suits homes that want a little definition without a full period look.
Flat casing is a square-edged board with no profile, and it is the go-to for modern and contemporary interiors. Its clean lines work well with minimalist doors and can be built up in width for a bold, architectural frame.
A back band is a small moulding added around the outer edge of flat or simple casing to give it more depth and a custom, high-end look. It is an easy upgrade that turns a plain casing into something more substantial without replacing it. See our back band trim collection for profiles that pair with our casing.
A back band adds a stepped shadow line at the outer edge of the casing, which makes the trim look thicker and more deliberate. It is a cost-effective way to get the presence of wide, milled casing while keeping a simpler, flatter face in the middle.
Casing comes in MDF, solid wood and pre-primed options, and the right choice depends on where it is going and how it will be finished. For most painted interior trim, MDF and primed casing give a smooth, consistent finish at a lower cost; solid wood is the pick for stain-grade work and higher-moisture or high-traffic areas.
MDF casing is engineered, dense and perfectly smooth, which makes it excellent for a painted finish. It has no grain or knots to telegraph through paint and is usually the most affordable option, which is why it is so common in new construction.
You can use MDF casing in a bathroom, as long as it is sealed and kept away from direct or standing water. Standard MDF swells if its edges are left raw, so proper sealing at every cut is the key. In a powder room or a well-ventilated bathroom, sealed MDF casing performs well; for a wet, poorly ventilated space, solid wood or a moisture-resistant board is the safer choice.
Every cut end of MDF should be sealed before installation, because the exposed core is the part most likely to absorb moisture. A coat of primer or a dedicated edge sealer on freshly cut ends stops water from wicking in.
For bathrooms, prime all faces and cut edges, then caulk the casing to the wall and jamb so moisture cannot reach the seams. Primer plus a quality paintable caulk is what keeps MDF trim looking crisp in a humid room.
Solid wood casing — usually pine or poplar — is the choice for stain-grade trim and rooms that need extra durability. Poplar takes paint beautifully and resists dents better than MDF, while pine is economical and can be stained or painted. Both handle humidity better than standard MDF.
Pre-primed casing arrives ready to paint, saving a step on site, while unfinished casing lets you stain the wood or control the primer yourself. If you are painting, primed casing is the faster route; if you want a natural or stained finish, choose unfinished solid wood.
Casing is sold by the linear foot, and how much you need comes down to the number and size of your openings. Standard casing widths run from about 2-1/4″ to 3-1/2″, though wider and built-up profiles are available for a more dramatic frame.
Most interior door and window casing falls between 2-1/4″ and 3-1/2″ wide, with 2-1/2″ a common all-round choice. Wider casing — or a narrower casing paired with a back band — reads as more formal, while narrower casing suits smaller rooms and modern spaces.
To estimate casing, measure the height and width of each opening and add for mitre cuts and waste. On a first pass it is quicker to allow a set amount per opening than to measure every piece to the inch.
As a rule of thumb, budget about 17 linear feet of casing per standard interior door (enough for both sides) and roughly 14–16 feet per window, then add about 10% for mitre waste. Bring your opening counts and sizes to the store and we will help you land on an exact quantity.
Casing, jamb and doorstop are three separate parts of the same opening, and knowing how they relate helps you order the right pieces. The jamb is the frame, the doorstop is the strip the door closes against, and the casing is the trim that covers the joint between the jamb and the wall. For the full explanation of how the three fit together, see our door jamb and doorstop moulding guides.
Installing casing comes down to setting a consistent reveal, cutting clean mitres and fastening without splitting the trim. The steps below are the same for door and window casing.
Start by marking a reveal — a small, even setback of about 3/16″ from the inside edge of the jamb — around the opening. A consistent reveal is what makes casing look intentional and gives the mitres room to line up.
Casing corners are joined with 45° mitre cuts so the profiles meet in a clean diagonal seam. Cut and test-fit each corner before nailing; small tweaks to the angle close up gaps caused by out-of-square openings.
Where casing ends without meeting another piece — such as the outer edge of a window stool — a mitre return folds the profile back on itself for a finished edge. Returns hide the end grain and look far cleaner than a squared-off cut.
Fasten casing with 15- or 16-gauge finish nails — one line into the jamb and one into the wall framing, spaced roughly every 16″. Set the nails, fill the holes, and caulk the inside and outside edges before painting for a seamless finish.
Prime first, then finish casing in a durable semi-gloss or gloss that stands up to cleaning and handling. A slight sheen also highlights the profile’s contours, which is what makes the trim read as a crisp frame rather than a flat board. Pre-primed casing needs only your topcoats; unfinished wood should be primed on all faces first.
Casing looks different in person than it does on a screen, which is why we encourage you to see and feel the profiles at our Markham or Etobicoke showrooms. You can compare Colonial, step bevel and flat profiles side by side, take a sample home to check it against your doors and lighting, and lean on our complimentary design consulting to match casing to your baseboards and overall style. Delivery is included on select orders, and our team is glad to help both homeowners and contractors get the specs right the first time.
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