Measure the width in three places and the drop in three places, then build the blind off the smallest width. That one habit prevents more problems than anything else, because almost no window in a Sydney house is perfectly square.
Decide where the blind is going to sit first
A roller blind either fits inside the window reveal or fixes to the wall or architrave in front of it. Inside the reveal looks tidier and keeps the blind out of the way. Face fixed gives you better light control, because the fabric runs past the glass on every side.
The two methods use different numbers, so make that call before you pick up the tape. Write the position on the same sheet as your measurements. Change your mind later and the deductions change with it.
Measuring inside the reveal
Take the reveal width at the top, the middle and the bottom, then use the narrowest of the three. Do the drop on the left, in the centre and on the right, and use the longest one so the fabric still reaches the sill.
Brackets need clearance for the tube to turn, so an inside mounted blind is always made smaller than the opening. We usually take 10mm off the reveal width in total, around 5mm a side. That leaves a thin light gap down each edge, which is one reason bedrooms are often better off face fixed.
Use a steel tape rather than a cloth one, and work in millimetres. Round the width down, never up.
Measuring for a face fixed blind
Here you are covering the window rather than fitting into it. Where the wall allows, add 150mm either side of the glass so the fabric overlaps and light does not spill around the edges. Set the top fixing at least 100mm above the opening so the roll clears the head of the window.
For the drop, measure from that fixing height down to where you want the bottom rail to finish. Running 50mm past the sill looks better than stopping level with it.
Check the reveal depth before you order anything
Depth decides what will physically fit. A standard single roller bracket wants about 60mm of reveal depth to sit fully recessed. A cassette needs closer to 100mm, and a double bracket carrying two rollers needs more again.
Think about the roll as well. Fabric builds up on the tube as it winds, so a long drop finishes fatter at the top. A 2700mm drop of blockout can roll up to roughly 80mm across, and all of that has to clear the architrave, the window handle and the reveal itself.
Tube size, and why width matters more than people expect
Roller tubes come in 32mm, 38mm and 45mm. Small windows run fine on 32mm. Wide blinds and long drops go on 38mm or 45mm, because a thin tube under heavy fabric bows in the middle and the fabric starts creeping to one side as it rolls.
That is a judgement call based on width, drop and fabric weight together. Get the width wrong on a wide window and you are not just short on fabric, you are on the wrong tube as well.
The drop deserves the same care. A blind cut 100mm short looks like a mistake from across the room, and one cut too long drags on the sill and wears a line into the fabric edge. Measure to where the bottom rail will actually finish, not to where the glass stops.
The details people forget
- Which side you want the chain or the motor. Chains usually go on the side away from a door swing or the head of a bed.
- Window handles, locks and flyscreen tracks, any one of which can foul a blind that fits perfectly on paper.
- Tiles, splashbacks and skirting that stop a bottom rail sitting flat against the wall.
- Child safety. Under the Australian rules a loose chain must not be able to form a loop of 220mm or more within 1600mm of the floor, so a cleat or tensioner gets fixed to the wall or frame at install.
Plaster, brick and tile all take a different fixing, so note what the wall above your window is made of while you have the tape out. It changes the plug, and on tile it changes the order of work.
If you would rather not chase a tape around the house, we measure for free and quote on the spot. Have a look through the roller blind range, the blockout options for bedrooms or a cassette headbox that hides the roll, then give us a call and we will bring samples to the window.
Common questions
Do I measure the window or the blind?
Measure the opening, always. Give us the reveal width and drop, or the wall to wall size if the blind is being face fixed, and tell us which mount you want. We apply the bracket deductions in the factory, so you should never take them off yourself.
How much light gap will an inside mounted blind leave?
Around 5mm each side, because the tube needs clearance to turn inside its brackets. In a living room nobody notices it. In a bedroom it shows up as two bright lines at sunrise, so face fixing or a cassette is the better call there.
Can a roller blind fit a shallow reveal?
A standard single roller needs about 60mm of reveal depth, and a cassette or a double roller needs closer to 100mm. If your reveal is shallower than that, the blind gets face fixed onto the architrave or the wall above the window instead.