Inside vs Outside Mount: Which Is Right for Your Window?
Before you measure a single window, you have to answer one question: will the blind sit inside the recess or outside it, on the wall or frame? It is the decision that shapes everything else — how you measure, how much light escapes, and how the finished window looks. Neither option is universally better; each suits particular windows and goals.
What each mount means
An inside mount fixes the blind within the window recess, so the treatment sits flush inside the opening. An outside mount attaches above the opening on the wall or window frame, with the blind overlapping the recess on all sides. The same blind can often be ordered either way; what changes is the bracket placement and the measurements you supply.
The case for an inside mount
Inside mounts give the cleanest, most built-in look. Because the blind sits within the frame, it shows off decorative moulding, leaves the sill clear for ornaments or a window seat, and layers neatly under curtains if you later add them. Designers often prefer it for exactly this tailored appearance.
The trade-off is that an inside mount needs a recess deep enough to take the headrail, and it inevitably leaves small light gaps down each side where the blind clears the reveal. For most living spaces that is fine; for a bedroom where you want total darkness it can be a drawback.
The case for an outside mount
An outside mount is the more forgiving and more light-blocking choice. Because it overlaps the opening, it covers the gaps an inside mount leaves, which makes it the better pick when darkness matters. It can make a small window look larger and taller, it hides an out-of-square or unattractive recess, and it works when the recess is too shallow for an inside fit. Deduct nothing for clearance here — instead you add coverage, typically a few centimetres on every side.
The downsides are mostly aesthetic and practical: the blind projects into the room a little more, it covers the surrounding moulding, and you need solid wall above the window to anchor the brackets.
How to choose
Work through these questions in order:
- Is the recess deep enough? Measure the depth and compare it with the blind’s minimum-depth spec. If it’s too shallow, an outside mount is your answer.
- How dark does the room need to be? For a nursery, bedroom, or media room, an outside mount — ideally with a blackout fabric — blocks far more light. Pair this decision with our Light-Blocking Opacity Selector.
- Is the window square and attractive? A neat, deep recess flatters an inside mount; a shallow, uneven, or plain one is better hidden behind an outside mount.
- What’s on the sill or frame? Handles, cranks, and a sill you want to keep clear all push you toward one option or the other.
Measuring follows the mount
Once you’ve chosen, the measuring method is fixed. For an inside mount, measure the exact opening — width in three places, taking the narrowest — and let the factory deduct the clearance. For an outside mount, measure the opening and add your chosen overlap. The Blind & Shade Size Calculator handles both: pick the mount type and it applies the right deduction or overlap automatically, so the size you order matches the window you have.
A quick rule of thumb
If you want a crisp, tailored look and the recess is deep and square, mount inside. If darkness, coverage, or a difficult window is your priority, mount outside. When you genuinely can’t decide, an outside mount forgives more and blocks more light — which is why it’s the safe default for bedrooms.