An inside mount sits the blind inside the window reveal, so the architrave still frames the window. An outside mount fixes the blind to the wall or the architrave and covers the opening, which blocks more light but takes up a little of the wall.
What the two mounts actually mean
The reveal is the recess between the face of your wall and the window glass. An inside mount, sometimes called a reveal fit, puts the brackets on the top or the sides of that recess. The blind finishes flush with the wall and the whole thing looks built in.
An outside mount, or face fix, puts the brackets on the wall above the window or on the front of the architrave. The blind hangs in front of the opening. It reads as a bigger blind, and it covers more.
Reveal depth decides most of it
Before anything else, measure how deep the reveal is. A slimline roller blind needs about 40mm of depth to sit clear of the architrave and run without touching. A roller with a cassette, or a double roller carrying two fabrics on one bracket, wants closer to 100mm.
Timber venetian blinds need room for the headrail and for the slats to stack when the blind is raised. Shutters need more again, because the frame itself takes up depth. If your reveal is shallow, the decision is already made and a face fix is the sensible answer.
Aluminium window frames in a lot of Sydney units sit almost flush with the plaster, which leaves nothing to fit into. Older brick houses with deep timber reveals are the opposite, and an inside mount usually looks better in them.
When an outside mount is the better call
Light control is the main reason. Fixed outside the opening with roughly 150mm of overlap past the glass at each side and above, a blockout roller blind gets a bedroom far darker than the same blind fitted into the reveal.
It also hides a lot. Out-of-square openings, chipped render, a window that sits off centre in the wall, an old air conditioner cutout. An outside mount covers all of it, where an inside mount follows every crooked line and shows it off.
A face fix is often the practical choice over a window that opens inwards, or where you need the blind to clear a handle or a flyscreen frame.
Light gaps, and what to do about them
Every inside-mounted blind leaves a light gap. It has to be cut narrower than the opening so it can run, so a thin strip of light comes down each side. In a lounge nobody notices. In a bedroom used during the day it is the first thing people complain about.
Three things reduce it. Mount outside the reveal with proper overlap. Add a cassette or a pelmet so light cannot spill over the top of the roll. Or run a curtain over the top of the blind to catch what gets past the edges.
Side channels are another option on some roller blinds, and they close the gap tightly, though they do add hardware down both sides of the window.
Face fix, ceiling fix and what is behind the wall
Where the screws go matters as much as the mount you choose. A timber architrave holds a bracket well. Plasterboard on its own does not, so brackets there need the right anchor or need to pick up the timber behind the lining.
Brick and render need a masonry plug. On full-height glass or stacker doors there is often no wall above the opening at all, and the blind goes to the ceiling instead. A ceiling fix needs a bracket landing on a joist or on solid backing, not into a sheet of plasterboard.
This is the part worth leaving to the installer. A bracket that pulls out of the wall six months later usually went into the wrong thing on day one.
Measuring and deductions
For an inside mount, measure the width in three places, top, middle and bottom, and use the narrowest figure. Old openings are rarely square. The blind then gets a small deduction so it runs without rubbing, usually around 10mm across the width, though it varies by product.
For an outside mount you are working the other way, adding overlap rather than taking it off. Add enough width to cover the opening and land the brackets on something solid, and enough drop that the blind finishes below the sill.
Deductions are the part homeowners get caught on, because a blind ordered at the exact reveal size will not fit. If you are measuring for a quote, give the raw reveal sizes and let whoever makes the blind apply the allowances.
If you are not sure which way to go at your windows, book a free measure and quote. We will check the reveal depth, look at what the walls are made of, and recommend the mount that suits each opening.
Common questions
Which mount looks better?
An inside mount usually looks neater, because the blind sits inside the reveal and the architrave still frames the window. An outside mount looks bigger and bolder, and it can make a small window appear larger. Both look fine when they are fitted straight and level.
How much overlap does an outside mount need?
Around 150mm past the glass at each side and above is a good working figure when you want to keep light out. Less than that and light finds its way around the edges. You also need enough wall to land the brackets on something solid.
Can I fit an inside mount if my reveal is only 30mm deep?
Not comfortably. A slimline roller wants about 40mm, and anything with a cassette wants closer to 100mm. At 30mm the blind will either foul the architrave or protrude past the wall face, so a face fix is the better outcome.