Window blinds should fit perfectly to your window’s measurements only when they are installed within the window frame referred to as an inside mount. If the blinds are typically wider than your window by a few inches or longer than the window, then the blinds are installed outside the window frame which is referred to as an outside mount. Every kind of mounting has its considerations and certain steps for measuring.
Selecting a Mounting Style
Blinds with an inside mount provide a clean look as the blinds fit tightly inside the window frame and don’t cover any of the window sill or the window casing. The blind itself is comparatively flush with the wall or trim, letting you add panels, curtains, or drapes over the blinds if desired.
Because of the snug fit, an inside mount works ideally for square windows. The window frame should offer enough depth for the blinds. Depending on the blind style, the window frame would require 1 1/2 to 3 inches or more depth to house the blind’s head rail.
An outside mount presents more installation choices compared to an inside mount. Outside mount blinds can be positioned onto the window casing, above the window, onto the sidewall, or even onto the ceiling. The blind can cover some or all of the window sill or trim, and it can extend below and above the window. Since an outside mount blind overlaps the window trim, it blocks out light better than the inside mounts. The main drawbacks of outside mount blinds are extending beyond the window plane or wall and obscuring the window casing.
Is It OK To Have Your Blinds Longer Than Your Window?
In most cases, it is OK to have your blind longer than your window, even for inside mount. This would just mean that your blind would have extra material that would stack on the sill. That said it isn’t exactly ideal as it won’t provide as clean of a look. For outside mounts on the other hand, you actually want to overlap your blind so that it is longer than your window as it will provide better light blockage.
There are some special cases for certain types of blinds. For example any vertical blind or shade should not be longer than the window on inside mounts, as then the slats or shade would be too long and would not fit. Similarly, on a Zebra Shade or Sheer Shade, the material is designed to have the stripes align and close when lowered to the sill. If you order the shade too long, it may not align properly when lowered to the sill of your window.
Measuring a Window for Inside Mount
An inside mount blind should fit the window measurements perfectly. Due to this, window blind users are always asked to measure the length and width of the window trim at three distinct places. For the blind width, measure straight across the top, middle, and bottom of the window opening and note down the minute measurements. For the blind length, you will have to vertically measure between the peak of the opening and the windowsill, at the right, left, and center of the opening. The longest measurement should be recorded.
While ordering blinds, provide precise window measurements of the window. Then, some amount, typically ¼ inch, will be subtracted by the manufacturer from the width of the blind so that it doesn’t rub along the sides of the window opening. Also, it is important to provide the depth of the window frame or the distance between the front face of the casing and the inside face of the window frame.
Measuring a Window for Outside Mount
These blinds mounted outside the window frame extend beyond the window trim at the sides and cover the opening at the window top. However, they can overlap the window casing as minimum or as much as you want. If the window frame projects from the wall, then the blind commonly stop at the peak of the window sill. Alternatively, the blinds may extend below the window sill if the sill doesn’t interfere with the blind’s operation.
Sizing of blinds for mounting outside the window is mostly an aesthetic choice, however, there are some measurements to verify before deciding on size. Measure between the peak of the window and the ceiling molding to ensure there is enough provision for mounting the blinds. Repeat the same for both the window sides by measuring between the window and any adjacent windows, doors, or walls. Lastly, to make sure of the light control as well as privacy, the blinds should be at least three inches broader than the window casing, so that it overlaps the window by 1 and a half inches on each side.
Why the Type Of Mounting Matters
There are three important things to think of while deciding on the type of mounting for your blinds:
There might be physical obstructions that will prevent blinds from working in a single position. For instance, there might be handles, locks, or mullions that avoid a blind from working correctly when mounted within the window sill. In such a case, we would recommend you outside mount your blinds.
- Light Block
Even though the size of the window is the same, a blind made for the inside mount will be smaller than the window opening and a blind made for the outside mount might be larger to conceal the whole opening. Sounds sensible, right? An inside mount blind will have a little gap between the window frame and the blind. This gap is due to the space needed for the mounting brackets which also provides the blind with sufficient space to function effectively without catching on the window sill. This gap lets a minimal amount of light pass through.
In A Nutshell
While there exist no set rules in terms of options for mounting blinds, it is essential to analyze the appearance as well as functionality that can be achieved with each of them. This way you can ensure that you are making a correct decision in buying window blinds that you will love in future years