The three widths you can actually buy, and why they differ<\/h2>\n\n![\"Three](\"\/blog\/wp-content\/uploads\/interior-door-casing-sizes-guide.jpg\")
door casing<\/strong> in 2-1\/4 inch, 3-1\/4 inch, and 4 inch widths laid side by side against a measuring tape on a workshop bench” width=”1280″ height=”720″ \/>The three widths that ship, shown against a tape. The label gives the nominal size, so check the actual face before you buy.<\/figcaption><\/figure>\nCasing is not sold in an open range of sizes. It comes as stock moulding.<\/p>\n
The widths in the standard range are what almost every mill<\/strong> and home centre carries.<\/p>\nThe narrowest of the three is 2-1\/4 inch<\/strong>. It is the traditional width for narrow trim work, and it is what you will find on houses built before the middle of the last century, when rooms were smaller and trim was scaled to match.<\/p>\nThe middle width, and the one most modern interior work uses, is 3-1\/4 inch<\/strong>. This is the default for a standard 2-1\/2 inch door casing and it suits the baseboard heights that came with post-war housing.<\/p>\nThe widest of the common widths is 4 inch and up. Wider casing started showing up when baseboards got taller and ceiling heights rose, and it pairs with the flat and Craftsman profiles rather than the narrow colonial ones.<\/p>\n
There is a practical floor under all of it. Moulding producers put a minimum on casing width because a board narrower than a certain point will not hold a mitre joint together properly.<\/p>\n
The mitre joint<\/strong> is where the whole piece fails first. National Hardwood, a hardwood moulding supplier, states that casing must be at least 2-1\/4 inches wide and be made in three pieces, with the head cut to fit between the two legs.<\/p>\nSo if you are shopping and the width looks odd, you are probably looking at something that is not really casing. Baseboard cap, brick mould, and door stop all get sold near the casing in a lumber yard, and they are not interchangeable.<\/p>\n
Nominal width, actual width, and the number on the label<\/h2>\n
Here is the part that catches people: the number on the box is a nominal width<\/strong>, and it is not the number you will measure across the face of the board.<\/p>\nMoulding is sold by its nominal size<\/strong>, which is a rounded reference figure.<\/p>\nThe actual face<\/strong> of the board, the part you see once it is on the wall, is thinner. A casing sold as 3-1\/4 inch may present a face that measures closer to 2-1\/2 inches across once the profile and the back bevel are taken into account.<\/p>\nThe profile is what causes the difference. A colonial casing with an ogee on the inside edge does not present its full width as a flat surface.<\/p>\n
That means it visually reads narrower than a flat casing of the same nominal size. This is why two pieces of the same nominal width can look like different widths on the wall.<\/p>\n
Measure the board face<\/strong> when you are matching existing trim, and measure it at the widest part of the profile, not at the thin edge.<\/p>\nHold the tape against the board before you buy and you will not be guessing.<\/p>\n
One more thing to know about the numbers. Casing is commonly sold in lengths of 12 feet<\/strong>, and in some markets in metric sizes instead of imperial.<\/p>\nA supplier working in millimetres<\/strong> will list the same board as 65 mm rather than 2-1\/2 inches. The conversion is not exact, because the imperial figure was always nominal, so ask for the actual face width either way.<\/p>\nHow wide should the casing be for your house<\/h2>\n
If you are matching an existing house rather than fitting out a new one, the rule is simple. Match what is already on the doors and windows of that same room.<\/p>\n
Match what is on the other rooms that read as one with it too. The windows and doors guide<\/a> covers how the pairing works across a whole house.<\/p>\nThe first reference is the window casing<\/strong>. Designers almost always pair door trim with window trim, so the doors should carry whatever width the windows in the room already carry.<\/p>\nWhen the two differ, the door is the thing that looks wrong. The window trim is what you look at while you are walking past.<\/p>\n
The second reference is the baseboard. The convention is that casing should be equal to or slightly narrower than the baseboard height in the same room.<\/p>\n
Wider than the baseboard<\/strong> casing looks unbalanced, because the eye reads the vertical trim at the door as heavier than the horizontal trim at the floor, and the two are in the same sightline.<\/p>\nThe third reference is the profile style, and this is where flat casing<\/strong> changes the calculation. Flat casing has no ornament, so it reads wider for its nominal size than a colonial profile does.<\/p>\nA flat 3-1\/4 inch casing next to a colonial 3-1\/4 inch casing will look like the flat one is the bigger board, even though the label says the same thing.<\/p>\n
If the room already has ornate trim, matching the weight of the profile matters as much as matching the number.<\/p>\n
The rule for the Craftsman profile is the opposite. It is a wide, chunky flat board by design, and it is meant to sit wider than the baseboard. If a house was built with a wide flat profile throughout, keeping that width is correct even when it breaks the baseboard rule.<\/p>\n
What the casing has to cover, and why that sets the minimum<\/h2>\n
Casing is not decoration on its own. Its job is to cover the joint where the casing meets the wall, and that joint has a physical width you cannot choose.<\/p>\n
On a new frame, the casing covers the edge of the rough opening<\/strong> and the nailing fin<\/strong> that the frame manufacturer left exposed for the trim to cover.<\/p>\nThe fin is typically 1 inch<\/strong> wide, and the casing has to sit over it entirely. That means the visible face of the casing has to be at least as wide as the fin plus the frame edge it covers.<\/p>\nOn an older house with plaster walls, the same joint is wider. Plaster is thick, and the casing often has to cover 2 inches of the return from the frame to the face of the wall.<\/p>\n
That is why old houses so often carry a wide flat casing on a plaster wall<\/strong>. The joint sets a minimum, and the minimum is why you cannot simply pick the narrowest width on the shelf.<\/p>\nThe other thing the casing has to hide is the 1-1\/2 inch<\/strong> gap between the trim and the wall surface on a standard frame, which is why a narrow casing on a wide joint leaves a shadow line that reads as an unfinished job no matter how carefully it is fitted.<\/p>\nHow wide that gap ends up being depends on how the frame was set, and the measuring guide<\/a> covers how to check what you already have before you commit to a width.<\/p>\nOn a replacement job where the frame is staying and the existing casing is being removed, measure what was there before you order anything. The old casing is a free sample of exactly what the joint needs, and it tells you the width and the profile in one look.<\/p>\n
Before you buy, measure these three things<\/h2>\n
Three measurements and one comparison, and you can order the right casing with confidence.<\/p>\n
\n- The opening width<\/strong> across the finished face of the casing, or across the casing itself if it is still on the wall.<\/li>\n
- The existing casing<\/strong> profile and its actual face width, measured at the widest point.<\/li>\n
- The paint finish<\/strong> on the existing trim, if you are matching. Semi-gloss on one wall and flat on another is the kind of difference nobody notices until it is done.<\/li>\n
- One check you can do in the aisle: hold the new board against the old one and compare the two faces directly, not the labels.<\/li>\n<\/ol>\n
Two of those decide the width. The opening width tells you the minimum you need, and the existing casing tells you what looks right in this room.<\/p>\n
If the two disagree, and they often do on a house that has been part renovated, the existing casing wins for appearance and the opening width wins for function.<\/p>\n
Split the difference, or use a casing profile<\/strong> with a narrower face and a backband<\/strong> to make up the width. That is the traditional repair for a wide joint.<\/p>\nOnce the width is settled, the fitting is a matter of length. That is covered in the casing installation guide<\/a>, along with how to cut the mitres so the joint closes properly.<\/p>\n
door casing<\/strong> in 2-1\/4 inch, 3-1\/4 inch, and 4 inch widths laid side by side against a measuring tape on a workshop bench” width=”1280″ height=”720″ \/>Casing is not sold in an open range of sizes. It comes as stock moulding.<\/p>\n
The widths in the standard range are what almost every mill<\/strong> and home centre carries.<\/p>\n The narrowest of the three is 2-1\/4 inch<\/strong>. It is the traditional width for narrow trim work, and it is what you will find on houses built before the middle of the last century, when rooms were smaller and trim was scaled to match.<\/p>\n The middle width, and the one most modern interior work uses, is 3-1\/4 inch<\/strong>. This is the default for a standard 2-1\/2 inch door casing and it suits the baseboard heights that came with post-war housing.<\/p>\n The widest of the common widths is 4 inch and up. Wider casing started showing up when baseboards got taller and ceiling heights rose, and it pairs with the flat and Craftsman profiles rather than the narrow colonial ones.<\/p>\n There is a practical floor under all of it. Moulding producers put a minimum on casing width because a board narrower than a certain point will not hold a mitre joint together properly.<\/p>\n The mitre joint<\/strong> is where the whole piece fails first. National Hardwood, a hardwood moulding supplier, states that casing must be at least 2-1\/4 inches wide and be made in three pieces, with the head cut to fit between the two legs.<\/p>\n So if you are shopping and the width looks odd, you are probably looking at something that is not really casing. Baseboard cap, brick mould, and door stop all get sold near the casing in a lumber yard, and they are not interchangeable.<\/p>\n Here is the part that catches people: the number on the box is a nominal width<\/strong>, and it is not the number you will measure across the face of the board.<\/p>\n Moulding is sold by its nominal size<\/strong>, which is a rounded reference figure.<\/p>\n The actual face<\/strong> of the board, the part you see once it is on the wall, is thinner. A casing sold as 3-1\/4 inch may present a face that measures closer to 2-1\/2 inches across once the profile and the back bevel are taken into account.<\/p>\n The profile is what causes the difference. A colonial casing with an ogee on the inside edge does not present its full width as a flat surface.<\/p>\n That means it visually reads narrower than a flat casing of the same nominal size. This is why two pieces of the same nominal width can look like different widths on the wall.<\/p>\n Measure the board face<\/strong> when you are matching existing trim, and measure it at the widest part of the profile, not at the thin edge.<\/p>\n Hold the tape against the board before you buy and you will not be guessing.<\/p>\n One more thing to know about the numbers. Casing is commonly sold in lengths of 12 feet<\/strong>, and in some markets in metric sizes instead of imperial.<\/p>\n A supplier working in millimetres<\/strong> will list the same board as 65 mm rather than 2-1\/2 inches. The conversion is not exact, because the imperial figure was always nominal, so ask for the actual face width either way.<\/p>\n If you are matching an existing house rather than fitting out a new one, the rule is simple. Match what is already on the doors and windows of that same room.<\/p>\n Match what is on the other rooms that read as one with it too. The windows and doors guide<\/a> covers how the pairing works across a whole house.<\/p>\n The first reference is the window casing<\/strong>. Designers almost always pair door trim with window trim, so the doors should carry whatever width the windows in the room already carry.<\/p>\n When the two differ, the door is the thing that looks wrong. The window trim is what you look at while you are walking past.<\/p>\n The second reference is the baseboard. The convention is that casing should be equal to or slightly narrower than the baseboard height in the same room.<\/p>\n Wider than the baseboard<\/strong> casing looks unbalanced, because the eye reads the vertical trim at the door as heavier than the horizontal trim at the floor, and the two are in the same sightline.<\/p>\n The third reference is the profile style, and this is where flat casing<\/strong> changes the calculation. Flat casing has no ornament, so it reads wider for its nominal size than a colonial profile does.<\/p>\n A flat 3-1\/4 inch casing next to a colonial 3-1\/4 inch casing will look like the flat one is the bigger board, even though the label says the same thing.<\/p>\n If the room already has ornate trim, matching the weight of the profile matters as much as matching the number.<\/p>\n The rule for the Craftsman profile is the opposite. It is a wide, chunky flat board by design, and it is meant to sit wider than the baseboard. If a house was built with a wide flat profile throughout, keeping that width is correct even when it breaks the baseboard rule.<\/p>\n Casing is not decoration on its own. Its job is to cover the joint where the casing meets the wall, and that joint has a physical width you cannot choose.<\/p>\n On a new frame, the casing covers the edge of the rough opening<\/strong> and the nailing fin<\/strong> that the frame manufacturer left exposed for the trim to cover.<\/p>\n The fin is typically 1 inch<\/strong> wide, and the casing has to sit over it entirely. That means the visible face of the casing has to be at least as wide as the fin plus the frame edge it covers.<\/p>\n On an older house with plaster walls, the same joint is wider. Plaster is thick, and the casing often has to cover 2 inches of the return from the frame to the face of the wall.<\/p>\n That is why old houses so often carry a wide flat casing on a plaster wall<\/strong>. The joint sets a minimum, and the minimum is why you cannot simply pick the narrowest width on the shelf.<\/p>\n The other thing the casing has to hide is the 1-1\/2 inch<\/strong> gap between the trim and the wall surface on a standard frame, which is why a narrow casing on a wide joint leaves a shadow line that reads as an unfinished job no matter how carefully it is fitted.<\/p>\n How wide that gap ends up being depends on how the frame was set, and the measuring guide<\/a> covers how to check what you already have before you commit to a width.<\/p>\n On a replacement job where the frame is staying and the existing casing is being removed, measure what was there before you order anything. The old casing is a free sample of exactly what the joint needs, and it tells you the width and the profile in one look.<\/p>\n Three measurements and one comparison, and you can order the right casing with confidence.<\/p>\n Two of those decide the width. The opening width tells you the minimum you need, and the existing casing tells you what looks right in this room.<\/p>\n If the two disagree, and they often do on a house that has been part renovated, the existing casing wins for appearance and the opening width wins for function.<\/p>\n Split the difference, or use a casing profile<\/strong> with a narrower face and a backband<\/strong> to make up the width. That is the traditional repair for a wide joint.<\/p>\n Once the width is settled, the fitting is a matter of length. That is covered in the casing installation guide<\/a>, along with how to cut the mitres so the joint closes properly.<\/p>\nNominal width, actual width, and the number on the label<\/h2>\n
How wide should the casing be for your house<\/h2>\n
What the casing has to cover, and why that sets the minimum<\/h2>\n
Before you buy, measure these three things<\/h2>\n
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