Six numbers. Three minutes. This is the part that decides whether it works.
Your blind is cut for one window and nothing else, so the measurements matter more here than on anything else you have bought for the bedroom. The good news is that there are only two dimensions and one rule.
Measure the opening three times across and three times down. Send us the smallest of each.
No window is truly square. Houses settle, frames swell, paint builds up in the corners. Across a normal opening the top and the bottom can differ by half an inch, and you will never see it by eye.
We build to the smallest number because a frame that fits the widest point cannot go in at all, while a frame built to the narrowest point slides in everywhere. The brush and weather strips are there precisely to close what is left over.
Depth first, then the six numbers
Use a steel tape, not a fabric one. Write each number down as you take it rather than trusting your memory for six of them.
The blind sits inside the opening, against the window stop, so measure the recess itself from painted surface to painted surface. Not the glass, not the outside of the trim, and not the old blind you are replacing.
Then measure from the glass out to the front edge of the opening. You need at least an inch and a half of clear depth for the frame to disappear into the wall.
Handles, latches, crank arms, alarm sensors, a trickle vent along the head. Anything that stands proud of the glass eats into the depth you just measured.
If you find one, measure the depth again from the front of the obstruction rather than from the glass, and use that number instead. Note what it is and where it sits when you order.
Hook the tape on the left side and read it against the right, keeping it level. Take one measurement just below the head of the opening, one halfway down, and one at the sill.
From the underside of the head down to the sill. Sills are often the least level surface in the room, so take the left and right edges as well as the centre and expect them to disagree.
Two numbers go on the order: the smallest width and the smallest height. Do not average them, do not round down for safety, and do not adjust for the strips. That is our job.
Put your six numbers in here
This does the arithmetic for you and tells you exactly what to type into the order. Nothing is sent anywhere.
Windows that need a second look
Tilt-and-turn handles stand proud of the frame. Measure to the wall as normal, then tell us where the handle sits and how far it protrudes. We set the frame forward to clear it.
The frame needs one and a half inches of depth to disappear into the opening. Anything less and we build it to sit on the face of the wall instead, which seals just as well and stands out slightly.
Measure each sash separately and order one blind for each. A single wide blind across a mullion never seals against the middle, which is exactly where the light comes in.
Roof and gable windows are built to order and need a photograph as well as numbers. Send both and we will come back with a drawing before anything is cut.
That is past the point where one frame stays rigid. We split it into two blinds that meet in the middle with an overlapping seal, and the join is invisible in the dark.
More than half an inch of variation across the opening means the window is properly out of square. Order to the smallest as usual and mention it, and we will send extra weather strip at no charge.
Five mistakes, in the order we see them
Every remake we have ever sent out came from one of these. None of them take longer than thirty seconds to avoid.
The most common one by a distance, and it costs you two to three inches on both dimensions. The tape belongs against the wall of the recess.
One number in the middle tells you nothing about the corners, and the corners are where light gets in. Three across, three down, every time.
Helpful instinct, wrong here. The factory takes the tolerance off your number, so a second deduction arrives as a visible gap on both sides.
Round to the nearest eighth, and when you are between two marks take the smaller one. Half an inch of generosity is enough to stop a frame going in.
Two windows in the same wall, built by the same joiner on the same day, are still two different sizes. Measure each one and label the numbers by room.
Get it wrong and we make it again
Custom means the risk normally sits with you. We would rather carry it ourselves, because a measuring mistake is the only thing standing between someone and a dark room.