Every blind or shade you buy asks the same question: inside mount or outside mount? Pick the wrong one and you get light leaking around the edges, a shade that doesn't fit, or brackets that won't hold. The good news: the right answer depends on your window, not on preference.
The quick verdict
Choose inside mount if your window frame is deep enough for the blind you want (check its minimum mounting depth), your frame is square and unobstructed, and you want a clean, built-in look that doesn't cover your trim.
Choose outside mount if you need better light blocking, have a shallow frame, want to hide frame imperfections, or have window cranks or decorative trim in the way.
Side-by-side comparison
Here's how the two mounting styles stack up across every factor that matters:
When you MUST use outside mount
Sometimes inside mount simply isn't an option. You need outside mount if any of these apply to your window:
- Shallow frame depth. Your frame is shallower than the blind’s minimum mounting depth. It won’t fit, and even if it squeezes in, the brackets won’t be secure.
- Window cranks or handles. Casement and awning windows have cranks or handles inside the frame. An inside-mounted shade will collide with them every time you operate the window.
- Tile or decorative trim inside the frame. If the interior of your frame has tile surround, stone, or decorative molding, there's no flat surface to mount brackets.
- Frame is uneven or warped. Older homes often have frames that aren't square. An inside-mounted shade will have visible gaps on one side or bind when you raise and lower it.
- Obstructions near the top of the frame. Alarm sensors, latches, or other hardware at the top of the frame can block bracket placement.
Pro tip
If your goal is maximum light blocking — for a nursery, home theater, or shift-worker bedroom — choose outside mount even if your frame supports inside mount. At least 2.5 inches of overlap on each side cuts the edge light gaps that inside-mounted shades always have. See our blackout vs. room darkening guide →
How to measure for inside mount
Inside mount requires precision. The shade must fit snugly inside your frame without binding or leaving gaps. Follow these steps, or use the order-size calculator to do the rounding for you.
- Measure the width at three points: top, middle, and bottom of the frame opening. Use the narrowest measurement. This ensures the shade won't be too wide to fit.
- Measure the height at three points: left side, center, and right side. Use the longest measurement. This ensures the shade fully covers the window at every point.
- Round correctly. Measure to the nearest 1/8 inch. If a reading lands on a 1/16 mark, round the width down and the height up.
- Check the frame depth. Measure from the front edge of the frame to the glass (or to a crank or lock that sticks out) at three points, and use the smallest. Compare it with the minimum mounting depth in the blind’s product specifications.
- Do not deduct for clearance. For inside mounts the factory makes the deduction. Order the exact measurements you take.
Common mistake
Do not round up your inside-mount width. A shade that is even 1/8" too wide will not fit into the frame. Always use the narrowest width measurement, rounded down to the nearest 1/8 inch.
How to measure for outside mount
Outside mount is more forgiving because you control the coverage area. Here's how to size it properly:
- Decide your overlap. Add at least 2.5 inches on each side of the window frame. Go wider for better light blocking, and check the product’s guide, since some brands suggest more.
- Measure the total width. Window frame width + overlap on both sides. For example, a 36-inch-wide window with 3 inches of overlap on each side = 42-inch-wide shade.
- Measure the height. From where you want the top of the shade (a few inches above the frame; check the product’s guide for bracket space) down to where you want it to end (at least the bottom of the frame, or lower for more coverage).
- Check for obstructions. Make sure the area above and beside the frame is clear — no vents, outlets, light switches, or adjacent windows that the shade would overlap.
Advantages of inside mount
- Clean, built-in appearance. The shade sits flush inside the window frame, giving a streamlined look that blends with the architecture.
- Doesn't cover decorative trim. If your windows have attractive molding or trim, inside mount lets it remain visible.
- Takes up less space. Nothing protrudes from the wall, which matters in tight spaces or when furniture sits near the window.
- Looks more custom. Inside-mounted shades look intentional and tailored, similar to built-in cabinetry.
Advantages of outside mount
- Superior light blocking. The overlap covers the gaps that inside mount can't avoid. This is why outside mount is the better choice for blackout applications. Nursery blackout guide →
- Makes windows appear larger. Mounting the shade wider and higher than the frame creates the illusion of a bigger window.
- Hides ugly or damaged frames. If your window frame is scratched, stained, or mismatched, the shade covers it entirely.
- Works on any window. No depth requirements, no square-frame requirements. If you have a wall above the window, you can outside mount.
- Easier for rentals. Screw holes in drywall above the window are simple to patch with spackle when you move out. Holes in the window frame itself are harder to repair and more likely to violate your lease. Renter-friendly blinds guide →
Rental tip
Before drilling into the window frame for inside mount, check your lease. Many landlords prohibit modifications to window frames specifically. Outside mount into the wall above is generally treated the same as hanging a shelf — small holes that are easy to fill. For a completely drill-free solution, look at tension-rod or adhesive-mount options. See no-drill options →
Our recommendation
Best budget blackout shade (works inside or outside mount)
Cordless Cellular Blackout Shade
From $22/window — available at Amazon, Target, and Walmart
See our top picks →
Frequently asked questions
What is the minimum frame depth for inside mount blinds?
There's no single number. Every blind lists its own minimum mounting depth in its product specifications, and it varies from product to product. Measure the depth at three points, use the smallest, and compare it with that product's minimum. If your frame is shallower, use an outside mount instead.
Which mount type is better for blocking light?
Outside mount is better for light blocking. By extending the shade at least 2.5 inches beyond the window frame on each side, and starting it a few inches above the frame, you cover the edge gaps where light typically leaks in. Inside mount leaves small gaps between the shade and the frame, which let light seep through.
Can I inside mount blinds in a rental apartment?
Inside mount requires drilling brackets into the window frame itself, which many landlords do not allow. Check your lease first. Outside mount drills into the wall or molding above the window, which is often easier to patch when you move out. For a completely drill-free option, consider tension-rod or adhesive-mount blinds designed for renters.