Curtains absolutely can make a room look smaller or larger, depending on their design. Thick curtains and dark curtains are known for making a regular room look slightly smaller, while sheer curtains made of lightly-colored fabrics are ideal for helping to visually expand a room's size.
Hang the Curtains as High as Possible
In order to make your window and the whole wall seem higher, put the curtain rod as high above the window as possible. Attaching the rail close to the ceiling tricks the eye into believing the wall is bigger. Thus, it visually expands the whole room.
Short curtains are typically only used when long curtains are unrealistic (such as when a radiator, the bed headboard, or some other object would interfere with the curtains). In addition, long curtains provide a better aesthetic and can make the room appear bigger, especially when hung higher than the window frame.
If you are interested in stationary panels, you will want your curtains to be long enough to lightly brush the floor, but not so long that they bunch up in a pile. A good rule of thumb is for your curtains to break anywhere from a ¼” to ½” from the floor, similar to a break in pant legs on your shoe.
A common rule for displaying curtains properly says the curtains finished width should be at least 2 times the width of your window (if not more - sheers can be 3 times the window width) to achieve a look of proper fullness.
Hanging long drapes on a short window is one of the easiest ways to increase the importance of the window and bring it into proportion to the room. Short drapes on a short window call attention to the size of the window and reduce the significance of the room, window and drapery style.
Sill Length
These are the shortest of the standard curtain lengths, which makes them a good opportunity to have some fun with pattern or color. Since they take up less visual space, you won't get tired of a bold choice.
Standard curtains come in three lengths—84 inches, 96 inches, or 108 inches. "Generally, you want to stay away from the 84 inch standard curtains unless you have very low ceilings.
If your curtain rod is too low, it'll shrink your window size and this is definitely something you do not want. Still unsure? A standard rule of thumb is about 4” up from the top of the window but you can definitely go up from there.
A rule of thumb (from Architectural Digest) is that curtains should be hung between four to six inches above the window frame, so install your curtain rod accordingly. When you hang the curtain rod high, it will make the window appear taller.
Curtains usually make a room look bigger than blinds do. Though blinds fit inside the window frame, the slats can often make a room feel shuttered and confined. Blinds also cast shadows across the room throughout the day, which means you don't get as much light as you could.
It depends on factors such as window length, but more often than not, curtains look best when touching the floor. However, how low you want your curtains to hang will determine what you want to achieve. In reality, different decorating styles employ varying curtain lengths.
Big floral patterns make a room appear larger. Install wallpaper with horizontal stripes to make a room seem wider, or commit to vertical stripes to stretch the room visually and raise the ceiling. A busy pattern featuring chevrons, simple geometric designs, or a texture that mimics marble can make a room seem bigger.
Floor length: Long curtains that go from above your window frame all the way to the floor to create a traditional, formal look. Typical curtain length for this style is 84 to 96 inches; these curtains will fall about 1/4-inch above the floor. They are ideal for living rooms, bedrooms and dining rooms.
Use contrasts and light colors that make rooms look bigger
Light and bright walls are more reflective, making a space feel open and airy, which helps maximize natural light's effect. Dark shades tend to absorb light, making rooms feel smaller. Accent walls to make a room look bigger is another way to go.
As a general rule of thumb, curtain width should be two to two-and-a-half times the width of the window. Curtains are typically sold as pairs, but you may need to double up depending on the size of your window.
Short Curtains
Visually speaking, high-water style is not the most appealing way to hang curtains. The shorter length can appear dated. Also, it can cut the visual height of your room in half. From a purely practical standpoint, however, short curtains are sometimes the best option.
One idea is to use a floor-length curtain to make short windows look taller. Hang them on stylish curtain rods installed at least 5 inches above the window frame. If your window is both short and wide, a medium-weight fabric is a better choice.
While fashion once dictated a “flood level” bottom line for curtains—one that hung just past the window sill, short enough that it would not get wet in a flood—today, style calls for curtains to either hang down to within ½-inch of the floor or even puddle slightly.
When you buy them in stores or online, there are two standard lengths: 84 inches and 95 or 96 inches. The length of the curtain dictates the height of the rod. If you buy 84-inch-long curtains, the rod must be mounted roughly 84 inches from the floor if the curtains hang from the rod without rings.
In Closing. For a 9-foot ceiling, 96-inch curtain panels are typically a good fit. This allows you to hang curtains that reach the floor, with the rod placed one foot from the ceiling. If you prefer curtains that pool on the floor or curtains that hang higher, just pick the next size up.
How Curtains Provide Insulation. Good curtains stop cold air from entering your home by creating an air gap between the room and the window. Ideally, they also prevent any flow of hot and cold air which would create a draft.
Go Vertical
Sheer, lightweight curtains with vertical stripes add height to a small space. Muted patterns or plaids in lightweight fabrics with bold vertical stripes or open-weave curtains with vertical designs woven into them add texture and airiness.