Inside vs Outside Mount Blinds: How to Choose, and How Each Changes Your Measurements

Inside vs outside mount blinds: the short answer

Inside mount puts the blind in the window box; outside mount hangs it on the wall or casing above the opening. That choice sets whether depth matters, whether the factory shaves your width or builds exactly what you type, and how much daylight gets around the edges.

Every depth and overlap figure below comes from SelectBlinds' product and measuring pages read on 2026-09-15, with the roller figure re-checked on the live page the same day.

What is an inside mount?

An inside mount puts the whole blind inside the window recess: brackets in the top of the opening, headrail between the jambs, casing visible around it. It is the tidier look and the default on most order forms.

It comes with two conditions. The recess has to be deep enough for the headrail, a per-product number, not a guess. And because the blind has to slide into a fixed opening and travel without scraping, the factory cuts it narrower than the opening you give it. That subtraction is the deduction, and SelectBlinds applies it for you: "We will make all the necessary deductions based on the measurements you provide. Do not make your own deductions. Don't add to the width to make up for any deductions that we will take." Its Premier cellular page adds the consequence: "Inside mounted shades may have slight gaps on the sides or top. For better light coverage, consider an outside mount."

What is an outside mount?

An outside mount hangs the blind on the surface around the opening: the wall above it, the face of the casing, or the ceiling. The blind is bigger than the window, and the extra width and height overlap the frame on every side. Depth stops mattering, because nothing has to fit inside the box.

What replaces depth is flat surface. SelectBlinds' roman measuring guide asks for "approximately 2 ½" of flat space" and its cellular guide for "at least 2 ½" of a flat surface"; its product pages say "at least 1-2½" of flat mounting space" and point to the Specifications tab for the exact figure. For an outside mount the seller builds what you type: "We'll custom make your shade to the exact dimensions you provide—no automatic additions are made." The overlap is yours to add.

How much depth do you need for inside mount blinds?

It depends on the product and the lift. Every SelectBlinds product page carries a "Dimensions by Configuration" table with two inside-mount columns, minimum depth and flush depth, and one outside-mount column, minimum space. What those tables say, by family:

Cellular shades need the least. SelectBlinds' Premier light-filtering cellular lists a 1 1/4-inch minimum inside-mount depth on its cordless lift, 2 1/4 inches to sit flush, and 1 inch of flat surface outside. On a continuous cord loop or a motorized wand the minimum drops to 3/4 inch.

Rollers depend on the headrail. SelectBlinds' Levolor blackout roller lists a 1 1/2-inch minimum inside-mount depth with an exposed roll and 2 1/2 inches to sit flush; with the cassette valance those become 2 1/8 and 3 5/8 inches. Outside, the exposed roll wants 1 1/8 inches of flat surface and the cassette 3 inches. Those figures were re-checked on the live page on 2026-09-15 and matched.

Romans change with the lift. SelectBlinds' Classic roman shades list 1 5/8 inches for the cordless lift and 2 3/4 inches for flush; the cord loop and motorized versions need 1 1/8 inches, 1 3/4 flush. The no-drill headrail on the same line needs 2 1/2 inches, more than either drilled option. The blackout roman guide covers the liner side.

Wood and faux wood need little to hang and a lot to disappear. SelectBlinds' Levolor 2-inch wood blinds list 1 1/4 inches to hang and 3 7/8 inches to sit flush, with 1/2 inch of flat surface outside; the Levolor 2-inch faux wood line lists the same three figures. The house lines differ; the table below has them. The wood vs faux wood comparison covers width ceilings and the moisture case.

Verticals need the most. SelectBlinds' Select Canvas vertical blinds list a 3-inch minimum, 4 1/2 inches for flush, and 2 inches of outside flat surface. Many sliding-door frames do not offer 3 inches of clear depth above the glass, which is why most verticals end up on the wall or ceiling; panel tracks are shallower, and the table has the Architect line. Both are in the sliding door measuring guide.

Minimum depth vs flush depth: which column do you read?

The two inside-mount columns answer different questions, and confusing them is how a blind that "fits" ends up looking wrong.

Minimum depth is the shallowest recess that will hold the brackets securely. Meet it and the blind hangs and works, but part of the headrail, and the stack when the shade is raised, sits proud of the casing. Flush depth is the recess that swallows the whole headrail so nothing projects past the frame. The gap is roughly the headrail's own depth, and on some products it is wide: the Levolor wood blind hangs in 1 1/4 inches but needs 3 7/8 inches to sit flush, so a 2-inch-deep frame gives you a working blind whose headrail stands out into the room.

Decide which look you want before you measure. If flush matters, the flush column is your minimum. Generic depth charts, including the one in the minimum mount depth reference, give one round number per product; the seller's table gives two per lift style, and the two can be inches apart.

Measure depth at the top of the opening, where the brackets go, from the front edge of the casing back to the glass or to whatever sticks out in front of it. Use a steel tape and round down; a recess a hair under a minimum is under it. The Measure & Mount Fit Checker shows the depth and deduction range for your product and mount.

What blocks an inside mount? Cranks, handles, tilt latches, and trim

Depth on paper is not depth you can use. Anything that projects into the recess in the path of the headrail or the moving shade takes its space away, and you measure to the front of that obstruction, not to the glass. Casement cranks are the classic problem; a folding handle helps, a fixed one at the sill can still catch a bottom rail. Tilt latches on double-hung sashes sit near where a headrail lands, and a bracket over a latch never gets screwed in. Sash locks, alarm sensors, and weatherstrip each steal a fraction of an inch that a minimum-depth mount does not have. Casing shape is the outside-mount version of the problem: beveled or rounded trim has no flat face for a bracket, so the mount moves up onto the wall or the ceiling.

SelectBlinds' Premier cellular configurator lists extension brackets and spacer blocks as yes/no options, and its Heritage wood page offers spacer blocks too; both hold the headrail forward of the mounting surface, which is how an outside mount clears a handle or a deep casing. Short of the minimum, you have three moves: a shallower product, a projection bracket, or the outside mount. The common measuring mistakes list starts with people who measured to the glass.

Are outside mount blinds better for blackout?

Yes, and the reason is geometry, not fabric. An inside-mount blind is cut narrower than its opening, so a blackout fabric that stops light dead still leaves a bright line down each side and a sliver along the top. Move the same fabric outside, overlap the frame, and those lines land on wall or casing instead of glass.

SelectBlinds' overlap guidance for width is to "add a minimum of two inches to each side, for a total of four inches, for the best coverage," and for height to "add at least two inches on the top and bottom, adding more depending on the amount of light coverage you're looking for." Its roman product pages go further because the fabric waterfalls over the headrail: "We recommend 4+ inches be added to the width of your shade when outside mounting to prevent light gaps." The bedroom blackout strategy puts the mount together with liners, side channels, and drapery; the outside mount is the cheapest piece of it.

How does the mount change what you measure and order?

Same window, two different sets of numbers.

Inside mount: measure the opening, type the opening. Width in three places, top, middle, and bottom, jamb to jamb. Height in three places, left, center, and right, top of the opening to the sill. SelectBlinds' general guide has you "round down to the nearest 1/8 inch" on width, round height up, and record width first. Which of the three you enter is a per-product rule (its roman guide says "Record the narrowest width of the 3 measurements," while the Premier cellular page says to "use the top measurement when ordering"), so read the page for your product. Then leave the number alone. The factory takes its deduction, published per collection with the note that deductions "may vary +/- 1/8"": 1/2 inch off the headrail and 1/2 inch off the fabric on the Classic roman, 1/4 inch off the headrail and 3/8 inch off the fabric on most cellular rows. Subtract any of that yourself and you double it; the blind arrives that much too narrow on a non-returnable order. Deduction rules explained covers the double-deduction trap.

Outside mount: measure the coverage, type the finished size. Start from the opening, or the outside edge of the casing if you want to hide it, and add the overlap on every side. For height, measure from where the brackets will sit to where the bottom of the blind should land: the sill, below the apron, or the floor for a door. What you type is what arrives.

Worked example. A 36-inch-wide by 48-inch-tall opening, square, with 1 3/4 inches of clear depth. Inside mount: order 36 by 48 and let the factory deduct. A cordless cellular, the exposed-roll Levolor roller, and the cordless Classic roman all clear their minimums; the cassette roller and the S-Wave faux wood do not, and the Levolor wood blind hangs but stands proud of the frame. Outside mount on SelectBlinds' rule: 36 plus 2 inches a side is 40 wide, 48 plus 2 inches top and bottom is 52 tall, so the order reads 40 by 52. The first-time measuring walkthrough has the tape-in-hand version; the cellular and roller guides add the product-specific rules.

Inside-mount depth by product line

All figures in inches, from SelectBlinds' product pages and measuring charts read on 2026-09-15. "Outside" is the flat surface the brackets need for an outside mount. SelectBlinds' caveat applies to every row: "Factory deductions and minimum depth requirements may vary based on feature options chosen when customizing your product."

Two things stand out. Cellular shades and cord-loop romans fit recesses nothing else will. And the flush column, not the minimum, decides whether a wood or faux-wood blind looks built in.

Choose inside mount when, choose outside mount when

Choose inside mount when the recess clears the flush depth for your product and lift, or clears the minimum and you accept the projection; the three width readings agree closely enough that a blind cut to the narrowest shows no wedge of daylight at the widest; nothing sits in the headrail's path; and you want the casing on show. Skip it when the depth is short by any amount, an obstruction eats the top of the recess, or the room has to be dark.

Choose outside mount when the frame is shallow, the opening is out of square, a crank or latch is in the way, the room is a bedroom or media room, the window is small and you want it to read larger, or it is a sliding door with no recess to speak of. Skip it when the casing is beveled with no wall above it to mount on, or the space between the casing and the ceiling or crown is less than the headrail plus the overlap.

If you are torn, the outside mount is the forgiving one. A width off by a fraction disappears into the overlap; the same fraction inside shows as a gap or a jam.

Which mount for renters and drill-free hardware?

Drill-free hardware does not free you from the mount decision; it forces one. Tension and lever systems grip the inside of the recess, so they are inside mounts by definition, and they need more depth than the screwed version, not less. SelectBlinds describes its Click2Fit option this way: "Click2Fit No-Drill Blinds secure the headrail in place with tension levers, offering a sturdy, damage-free mounting option." On the Premier cellular, both cordless lifts (Lift & Lock, and its top-down/bottom-up version) with Click2Fit are "only available with 2 1/2" or more window depth"; on the Classic roman, the no-drill headrail lists 2 1/2 inches against 1 5/8 for the drilled cordless version.

A renter with a shallow frame is in a bind: the recess cannot take the no-drill hardware, and the outside mount needs screws. The workable answers are a light shade on adhesive or magnetic brackets, or a landlord conversation about four small holes. The drill-free options guide sorts the systems by what they will hold.

Before you order either mount

Three things hold for every seller, not just the one quoted here. Every seller applies its own deductions and publishes its own depth table, so a figure from one site says nothing about another. Custom blinds are made to your size and generally not returnable; SelectBlinds' returns page says it plainly: "because all of our blinds and shades are custom made, we cannot offer a refund or exchange (remake) unless a product is defective." And policy text is perishable, so read the page on the day you order.

SelectBlinds' safety net for a measuring mistake is its FIT Protection, selected at no charge at checkout: a claim within 90 days of purchase, a corrected size within 2 inches per side of the original, one remake per product and four per household lifetime, with remake shipping charges applying. Its terms list improper installation or mounting method among the exclusions, so do not plan on it to turn an inside order into an outside one. The SelectBlinds review reads the whole policy set.