An inside mount fits a blind or shade within the window frame; an outside mount attaches to the wall or trim beyond it. Choose an inside mount for a clean, built-in look when the frame is deep and unobstructed, or an outside mount when you want more light control, added privacy, or a solution for a shallow or irregular frame.
What the Two Mounts Mean
“Mount” describes where a window covering is attached, not the type of blind or shade. With an inside mount, the headrail or mounting hardware sits inside the window opening, and the covering hangs within the frame. With an outside mount, the hardware is fixed to the wall, ceiling, or window trim, and the covering extends across the opening from the outside.
Both approaches can work with many kinds of blinds and shades. Their practical differences come from the window’s shape, available mounting surface, desired appearance, and how much coverage you need. An inside mount reveals more of the frame and surrounding wall. An outside mount covers more of them and can make the window covering appear larger.
How an Inside Mount Works
For an inside mount, the installer measures the width and height of the usable opening and attaches the brackets to the inside surfaces of the frame. The covering then moves up and down within that opening. Depending on the product, the brackets may attach to the top of the frame, its sides, or both.
The frame needs enough depth for the hardware and, in some cases, for the covering to sit without hitting the glass, handles, or other obstructions. Product instructions specify the minimum depth needed for installation and for a fully recessed fit. These are not always the same: a covering may fit inside a frame but project slightly beyond it.
Inside mounts often suit windows with attractive trim or a deep, square opening. They can also work well when several windows sit close together, because each covering stays within its own frame rather than spreading across the wall. A drawback is that small gaps may remain along the edges, allowing some light through. The size of those gaps depends on the design and fit of the covering.
How an Outside Mount Works
An outside mount places the brackets on a flat surface outside the opening, commonly the wall above the frame or the trim itself. The covering overlaps the window and may extend beyond its sides and top. The installer chooses the placement and overlap according to the covering’s design, the available surface, and the amount of coverage desired.
Because an outside mount covers more of the opening, it can help reduce light entering around the edges compared with an inside mount. It is often useful when the frame is too shallow for the hardware, when the opening is uneven, or when the window has an obstruction that would interfere with an inside-mounted covering. It can also hide unattractive trim or make a small window look more substantial.
The trade-off is that the covering is more visually prominent and takes up wall or trim space. It may overlap nearby molding, switches, furniture, or another window covering if its position is not planned carefully. An outside mount also needs a suitable surface for secure brackets; wall material and the location of framing can affect how the hardware should be fastened.
Side-by-Side Comparison
- Appearance: Inside mounts look integrated and leave the frame visible. Outside mounts create a larger visual shape and conceal more of the frame.
- Light at the edges: Inside mounts can leave visible gaps beside the covering. Outside mounts can overlap the opening to reduce those gaps, although no mount guarantees complete darkness.
- Frame requirements: Inside mounts need adequate depth and a workable opening. Outside mounts need enough space and a reliable surface beyond the opening.
- Window shape: A regular, deep frame often favors an inside mount. A shallow, uneven, or obstructed frame may favor an outside mount.
- Visual coverage: An inside mount shows more trim and glass. An outside mount can conceal trim and make the covered area appear larger.
- Measurement: Inside measurements are taken within the opening. Outside measurements define the overall area the covering should span.
Neither choice is automatically better. A neat, recessed appearance may matter more than edge coverage in one room, while privacy and reduced light leakage may matter more in another. The best choice is the one that fits both the window and the room’s priorities.
How to Choose for Your Window
Start by checking the frame rather than choosing by appearance alone. Look for adequate depth, a reasonably square opening, and clear space where the brackets and moving parts must sit. Check for handles, locks, cranks, window stops, and trim that could obstruct the covering. If the window opens inward, consider whether the treatment will interfere with its operation.
Then decide how much of the frame you want to show and how much of the opening you want to cover. An inside mount makes sense when you like the trim and want the covering contained within it. An outside mount is worth considering if you want broader overlap, need to conceal the frame, or cannot fit the hardware inside.
Also consider what is around the window. A deep sill, nearby cabinets, adjacent windows, or wall-mounted controls can constrain where an outside covering goes. A protruding handle or shallow frame can make an inside mount impractical. When a window has unusual angles, a curved top, or a very uneven opening, check whether the chosen product can be installed in either way before ordering.
- Choose an inside mount when the frame has enough depth, the opening is usable, and a low-profile appearance is the priority.
- Choose an outside mount when the frame is shallow, you need to cover more of the opening, or you want to conceal the trim.
- Pause and check the product instructions when an obstruction, unusual window shape, or limited mounting surface complicates either option.
Measuring and Ordering
Measuring rules vary by covering and mounting method, so use the instructions for the specific product rather than assuming one universal deduction or overlap. Some manufacturers make adjustments to inside-mount dimensions during production; others require the customer to provide particular finished dimensions. Do not subtract a guessed amount unless the instructions tell you to.
For an inside mount, measure the opening at the locations specified in the instructions. Frames can be slightly out of square, so a measurement at one point may not match another. Record the measurements as requested and check the frame depth at the bracket locations. The product instructions will clarify whether the narrowest width, a particular height, or another convention is required.
For an outside mount, first decide how far the covering should extend beyond the opening, then measure the total intended width and height. Account for the mounting surface and anything that might be covered or blocked. If the covering is intended to clear trim or overlap it, confirm the relevant dimensions before ordering. For a costly or complicated installation, a professional measurement can reduce the risk of an unsuitable fit.
Light, Privacy, and Room Use
Mounting location affects coverage, but it does not determine how opaque the fabric or slats are. A light-filtering shade may still admit substantial light when mounted outside, while a room-darkening product can still have edge gaps when mounted inside. If controlling light is important, consider the product’s material and construction along with the mount.
Privacy depends on the covering, its position, and the view from outside. A covering that fits inside the frame may leave narrow sightlines at its edges, while an outside mount can cover those areas more fully. The direction of slats, the opacity of a shade, and how it is operated also affect privacy. Check the view from the relevant neighboring spaces rather than assuming the mounting style alone will solve the issue.
In a bedroom, someone may prioritize reduced light around the edges. In a living room with decorative trim, preserving the frame may be more important. In a kitchen, handles and frequent window use may guide placement. These are practical considerations rather than fixed rules: the best arrangement depends on the actual window and how the room is used.
Common Problems and Misconceptions
A common mistake is assuming every inside mount is fully recessed. It may project into the room if the frame is not deep enough, even when the covering technically fits within the opening. Check the product’s depth requirements and clarify whether they describe a minimum fit or a fully recessed installation.
Another misconception is that an outside mount always blocks all light. It can reduce edge gaps when it overlaps the opening, but light may still pass through the material, between slats, or around the covering. The result depends on the product and installation.
People also sometimes measure the visible glass rather than the opening or overall area required by the mounting method. Those dimensions are not necessarily the same. Measuring the wrong surface can lead to a covering that is too small or cannot be installed as intended. Follow the product’s measurement diagram, and confirm which dimensions to submit before placing an order.
Installation and Safety Considerations
Mounting brackets need to be secured to a suitable surface with hardware appropriate to that surface. A wall-mounted covering may require different fasteners from one attached to solid wood trim. Follow the installation instructions, and seek qualified help if you are unsure about the wall, the bracket placement, or whether the proposed fasteners can support the product.
Keep window-covering cords and chains away from children and pets, and follow the product’s safety instructions. Cordless designs are an option for people who want to avoid exposed operating cords. Do not choose a mount solely for appearance if it places controls where they are difficult to use or creates an avoidable hazard.
Frequently Asked Questions
Which mount blocks more light?
An outside mount can cover more of the opening and reduce light entering at the edges. The fabric or slat design matters too, and neither mounting style alone guarantees a dark room.
Can I use an inside mount if my window frame is shallow?
Only if the covering’s hardware fits within the available depth and does not interfere with the glass, handles, or operation of the window. Check the product’s depth requirements; otherwise, an outside mount may be more suitable.
Does an outside mount make a window look bigger?
It can make the covered area appear larger because the covering extends beyond the frame. The visual effect depends on how it is positioned and the surrounding wall and trim.
Can an inside mount work with uneven windows?
Sometimes, but a frame that is out of square can create uneven gaps or complicate installation. Measure as the product instructions specify, and consider an outside mount if it can cover the irregular opening more effectively.
Should the covering be mounted on the trim or the wall?
That depends on the available mounting surface, the product’s bracket design, and the desired position. Follow the installation instructions and ensure the surface and fasteners can support the hardware.
Bottom Line
An inside mount keeps the covering within the window frame and suits openings with enough depth when a contained appearance is the goal. An outside mount extends beyond the frame and is often preferable for shallow or obstructed openings, broader coverage, or concealed trim. Measure according to the specific product instructions, consider light and privacy needs, and check the mounting surface before deciding.