When you're shopping for new blinds, one of the first decisions you'll face has nothing to do with colour or material — it's about how the blinds attach to your window. Should you go with an inside mount or an outside mount? It's a surprisingly important choice, and getting it right can make the difference between a polished, professional look and blinds that feel a little off.
The good news is that this isn't complicated once you know what to look for. Here's everything you need to know about inside and outside mounts so you can choose the right option for every window in your home.
What Is an Inside Mount?
An inside mount means your blinds are installed inside the window frame, sitting within the recess of the window. The blind fits snugly into the opening, creating a clean, built-in look that shows off your window trim.
When Inside Mounts Work Best
Inside mounts are the go-to choice for homeowners who want a sleek, minimalist look. They work beautifully when your window has a deep enough recess (usually at least 2 inches), you want to showcase decorative window casing or trim, or you prefer blinds that look built-in and architectural. They're also great in smaller rooms where bulky window treatments would feel out of place.
Inside mounts are particularly popular in modern and Scandinavian-style homes where clean lines are a priority. They also work well in bedrooms and bathrooms where a tidy, unobtrusive appearance is appreciated.
Limitations of Inside Mounts
The main limitation is window depth. If your window doesn't have enough recess, the blind may stick out awkwardly or the headrail may be visible from the side. You also need to measure very precisely — inside mount blinds need to fit accurately, with little room for error.
Another consideration: inside mount blinds don't provide the same level of light blockage around the edges. There will naturally be small gaps between the blind and the frame, which can let in light at the sides. If total darkness is a priority — especially in a bedroom — this is worth thinking through before you order.
What Is an Outside Mount?
An outside mount means your blinds are mounted on the wall or on the outer edge of the window frame, covering the window opening from the outside. The blind extends beyond the window itself, overlapping the frame on all sides.
When Outside Mounts Work Best
Outside mounts are the more versatile of the two options. They're a great choice when your window is shallow and doesn't have enough depth for an inside mount, when you want to maximize light blockage for a blackout effect, or when you want to make a window appear larger than it actually is. They're also ideal when the window has an awkward handle or crank that would get in the way of an inside-mounted blind.
Outside mounts are a solid choice for living rooms and kitchens where you want the window treatment to make a visual impact. By mounting the blind higher and wider than the actual window opening, you can dramatically change how spacious and airy a room feels.
Limitations of Outside Mounts
Outside mounts do cover your window trim, which may not be ideal if you have beautiful casing you want to show off. They can also feel less integrated in certain design styles. Measuring is a bit more flexible than inside mounts, but you still need to plan the overlap carefully — typically 1.5 to 3 inches on each side — to avoid light gaps and ensure full coverage.
How to Measure for Each Mount Type
Measuring for an Inside Mount
Measure the width of the window opening at three points — top, middle, and bottom — and use the smallest measurement. This ensures the blind will fit without forcing. For height, measure from the top of the opening to the sill at three points and use the longest measurement.
Most blind manufacturers will deduct a small amount (called a "deduction") from your inside mount width to ensure the blind fits cleanly inside the frame. Check with your retailer on their specific policy before ordering.
Measuring for an Outside Mount
For an outside mount, you have more control. Decide how much you want the blind to overlap the frame on each side — a minimum of 1.5 inches per side is recommended for good light control — and add those overlaps to your window width. For height, measure from where you want the top of the blind (often 3–4 inches above the window frame) down to where you want it to end, whether that's just below the sill or all the way to the floor.
Which Mount Type Is Right for You?
The honest answer is: it depends on your window and your goals. Choose an inside mount if you have deep window frames, love a clean minimalist look, and want to show off your trim. Choose an outside mount if you want maximum light blockage, have shallow frames, or want your windows to look larger.
When in doubt, outside mount is the more forgiving option — it covers more of the window and gives you more wiggle room on measurements. Many Canadian homeowners with older homes default to outside mount because older windows often don't have the depth needed for a true inside mount installation.
Frequently Asked Questions
Can I use the same blind for either mount type?
Many blinds and shades can be ordered for either mount type — you just specify your preference when ordering. Some specialty products may have specific requirements, so always confirm with your retailer before purchasing.
What if my window isn't perfectly square?
If your window is out of square — common in many older Canadian homes — an outside mount is usually the better choice. It's easier to compensate for irregularities when you're mounting outside the frame rather than trying to fit a blind snugly inside an uneven opening.
Do inside mount blinds always have light gaps?
There will typically be small gaps at the sides, but many products — like cellular shades or blackout roller blinds — are designed to minimize this. For true blackout conditions, consider pairing an inside mount blind with side channels, or choose an outside mount with generous overlap on all sides.
Can I change my mind after ordering?
Custom blinds are cut to size, so switching mount types after the fact is rarely possible. Make sure you're confident in your choice before placing your order. If you're unsure, a free consultation with a window treatment specialist can save you a lot of hassle — and money.
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