Of all the data that arrives with a wholesale order, the dimension is the only one that cannot be corrected afterwards. A colour can be changed, a mechanism repacked, a deadline moved — but once fabric has been cut to the wrong size, it is waste. There is no reworking it, and no shortening it without losing the properties of the system.
That makes measuring the one step in the whole chain where five minutes of attention pay for themselves a hundred times over. This guide is written for our wholesale partners — blind retailers, contractors and specifiers who go on site and measure themselves. We are a factory and we work exclusively in wholesale: we do not attend site measurements and we do not carry out installation. The dimension you send us is the dimension we manufacture to.
Before you reach for the tape: four checks
The most expensive mistakes do not happen during the measuring itself, but before it — because something was measured that was not yet ready to be measured.
1. The window must be physically installed
A drawing dimension and a site dimension are not the same thing. The opening is built with a tolerance, the window is fitted with a tolerance, the reveal is plastered with a tolerance — and those three tolerances add up. A two-centimetre difference from the drawing is routine, not an exception. Never measure from a drawing.
2. The direction and mode of opening
An inward-opening sash swings into exactly the space where the blind is meant to hang. With recess mounting this is the single most common reason a system cannot be used after installation. Check tilt opening as well — in the tilted position the top edge of the sash reaches further into the room than people expect.
3. Reveal depth
Recess mounting requires enough depth for the cassette or the tube with the rolled-up fabric to sit inside the opening without the fabric touching the glass or the hardware. If the depth is insufficient, the decision changes to face mounting — and it has to change before measuring, because the procedure is different.
4. Obstructions in the blind zone
Window handles, internal sills, ventilation grilles, radiators, indoor air conditioning units, cabling and lighting above the opening. Anything that enters the path of the fabric should be listed and added as a note to the position.
A practical rule: if walking up to an opening produced nothing but two numbers, you have probably missed something. A good measuring sheet carries a short note with every position.
Recess or face mount — decide before measuring
This is the one decision that changes the entire measuring procedure. Making it after measuring means measuring again.
| Recess mount | Face mount | |
|---|---|---|
| Where the system sits | Inside the opening, within the reveal | Over the opening — on the wall or on the frame |
| What is measured | The clear opening, smallest measured value | The opening plus overlap at the sides and above |
| Advantage | Clean appearance, the system stays flush with the wall and clears curtains and furniture | Better blackout, covers an uneven opening, independent of reveal depth |
| Drawback | Light gaps along the side edges, requires sufficient depth | The system is visible on the wall, needs free wall above and beside the opening |
| Typical use | Offices, commercial interiors, windows with deep reveals | Bedrooms, hotel rooms, openings without a reveal |
Measuring at three points — a rule with no exception
An opening is never perfectly rectangular. A difference of five to fifteen millimetres between the top and bottom width is a normal consequence of installation, and it is enough to stop a system entering the opening, or to make the fabric rub on one side.
- Measure the width at three points: near the top of the opening, in the middle and near the bottom.
- Measure the height at three points: along the left edge, in the middle and along the right edge.
- For recess mounting take the smallest measured value — it is the only one that guarantees the system passes along its full length.
- For face mounting start from the largest measured opening value and add the overlap to it.
Use a rigid steel tape, not a fabric one. A fabric tape sags and easily produces a five-millimetre error over two and a half metres. For heights above two metres, measure with two people or use a laser distance meter.
How each system is measured
The three-point principle is shared. What differs is exactly what goes into the dimension — on some systems the mechanism is wider than the fabric, on others the guides are part of the structure.
Roller blind
On a roller system the overall system width is always greater than the fabric width, because the brackets and the mechanism take up space on both sides of the tube. This means the visible fabric is narrower than the opening — something clients often report as a fault, although it is a structural necessity.
The height is measured from the point where the bracket sits to the point where the fabric should end. If the blind runs to the window board, measure to the board; if it runs past it, add the overlap beyond the board edge. State which of the two applies.
Zebra blind
In measuring terms a zebra behaves like a roller — the same bracket logic, the same tolerances, the same difference between system dimension and fabric dimension. What differs is that a zebra has a double fabric being wound, so the roll on the tube is thicker than on a roller system. In shallow reveals that can be decisive: check that the rolled-up zebra does not touch the glass or the hardware.
ZIP system (external)
On a ZIP system the side guides are not an accessory but a load-bearing part of the structure — the fabric is held inside them along its full height, and that is what gives the system its wind resistance. So you do not measure the glazed area alone, but the entire space available for the cassette and both guides.
Always state the substrate material the system will be fixed to. Concrete and a steel sub-structure are fine; timber moves with temperature and moisture and calls for a different solution. ZIP also works on rectangular geometry only — flag trapezoidal and arched openings in advance.
Wooden venetian blind
With venetians the slat width is chosen alongside the dimension, and it affects the space needed for the raised slat stack at the top of the opening. A wider slat means a taller stack. If the opening is restricted at the top — by a shutter box, a beam or a dropped ceiling — check that the raised stack does not cover more of the glass than the client expects.
For sloped and non-standard openings a venetian is more flexible than a roller system, but every such position needs to be flagged separately, not just entered as two numbers in a table.
Tolerances: who calculates them
This is where the largest share of wholesale complaints originates, and almost always through a misunderstanding rather than a measuring error.
Our rule is simple: the partner sends the clear opening dimension and the mounting type, and production applies the factory tolerances. If you deduct the tolerances yourself before sending and do not say so, the tolerance is applied twice and the system comes out too small for the opening — typically by one to two centimetres in width.
If for any reason you are sending an already calculated finished system dimension, it must be stated explicitly in the order — for example "system dimension, tolerances already deducted". Without that note, every dimension is treated as an opening dimension.
Record all dimensions in millimetres and without rounding. Rounding up on a recess mount is a direct route to a system that will not fit the opening.
Six most common measuring mistakes
One dimension for "identical" windows
Five windows on the same façade, apparently identical, one gets measured and multiplied by five. In practice they differ by a few millimetres because of installation tolerances. Solution: every opening is its own position with its own dimension, even when the numbers turn out identical.
Measuring before the window is installed
The order is placed from the drawing to save time. The window goes in with a difference, the blind does not fit, and both time and material are lost. Solution: measuring starts only once the window is in the wall.
The forgotten window handle
On a recess mount the fabric drops as far as the handle and stops there. The client ends up with a blind that will not close fully. Solution: measure how far the handle protrudes from the sash and compare it with the reveal depth. If it does not clear, it becomes a face mount.
An undefined bottom point for the height
"Height 160 cm" does not say whether the blind stops at the window board, runs past it, or drops to the floor. Three different products, one identical number. Solution: always state where the fabric ends alongside the height.
Width and height swapped
On narrow, tall openings a swap in the table goes unnoticed right up to production. Solution: stick consistently to the width × height format in every document, in the email as well as in the table.
Control side and roll direction left open
A chain on the wrong side means a blind that operates behind a door or across a work surface. Roll direction affects how close the fabric sits to the glass. Solution: enter both in the position; do not leave them to "whatever you think is better".
Open a wholesale account
We work exclusively with businesses — blind retailers, contractors and specifiers. Send an enquiry and receive wholesale terms and the measuring sheet in the format we use in production.
Send an enquiry →What to send with the order
A complete position contains seven items of data. If even one is missing, the order waits for it to be supplied — and that is a lost day in production.
| Data | Example | Why it matters |
|---|---|---|
| Position reference | P-03, office 2, left window | So that on site it is clear which package goes to which opening |
| System type | Zebra / roller / ZIP / venetian | Determines the whole manufacturing route |
| Dimension in mm | 1180 × 1640 (width × height) | No rounding, and always in the same order |
| Mounting type | Recess / face | Determines how tolerances are calculated |
| Control side | Left / right, viewed from inside the room | The wrong side makes the blind unusable |
| Roll direction | Close to glass / away from glass | Affects the clearance between fabric, hardware and glass |
| Note | AC unit 20 cm above the opening | Obstructions, unusual geometry, special requirements |
For any position you are unsure about, send a photograph of the opening with a tape measure in the frame. A photograph does not replace a dimension, but in nine cases out of ten it settles the question without a second site visit.
Frequently asked questions
Do I send the opening dimension or the finished blind dimension?
Always the opening dimension, with the mounting type clearly stated. Tolerances are calculated by production. If you exceptionally send a finished system dimension, say so explicitly — otherwise the tolerance is deducted twice.
Why is the smallest dimension used for recess mounting?
Because the opening is not rectangular. The largest dimension describes only the widest part of it; a system built to that will not enter at the narrower part. The smallest dimension is the only one that passes along the full height.
How much overlap should a face mount have?
The overlap is added on both sides and above the opening to reduce light gaps along the edges. How large it can be depends on the available wall and the bracket position — the rule is to make it as generous as possible, but without running into an obstruction during operation.
How is a ZIP system measured?
Measure the total space available for the cassette and both side guides, because the guides are a load-bearing part of the structure. Always state the substrate material the system will be fixed to.
What about arched or trapezoidal openings?
Roller, zebra and ZIP work on rectangular geometry. The solution is usually face mounting over a rectangular zone, or splitting into several positions. Flag such openings before sending the order, not together with it.
What if a dimension turns out wrong anyway?
If the error is ours, we correct it without discussion. If the dimension arrived wrong in the order, the fabric has already been cut and cannot be returned to its original state — which is exactly why this guide exists.
Conclusion
Measuring is not complicated — what is complicated is staying consistent at the twentieth opening of the same day, when everything already feels familiar. Almost every complaint that arrives as "the dimension is wrong" traces back to one of three things: it was measured before the window was installed, it was measured at one point instead of three, or the mounting type was never written down.
If you take only one thing from this text, make it this: send the clear opening dimension in millimetres, measured at three points, with the mounting type stated. The rest is our job.