Every made-to-measure range has a biggest blind it will make, and a smallest. The limits sit quietly on the order form until you type in a wide opening and the form refuses, so it pays to know why they exist and what your options are when a window falls outside them.
Why size limits exist at all
Four practical things set the ceiling.
- Fabric comes on rolls. Blind fabric is woven and coated in fixed roll widths. A blind wider than the roll would need a seam, and makers avoid seams because a join puckers, shows against the light and wears unevenly. The roll caps the blind, and roll widths differ even between fabrics in one range.
- Long roller tubes bow. A roller blind winds onto a tube supported only at its ends, and the longer the tube, the more it sags in the middle under its own weight and the fabric's. Past a certain span the sag makes the fabric run off line or creep to one side as it rolls. Wider rollers use fatter, stiffer tubes, but every tube has a span it cannot sensibly exceed.
- Headrails have limits. Verticals and venetians hang from an aluminium headrail. On a vertical, each louvre hangs from its own small carrier, so the weight is spread along the track and nothing is lifted in one piece - one reason verticals span the widest openings. A venetian must lift its whole stack of slats, which gets heavy quickly as the blind grows.
- Lifting mechanisms carry the load. Chains, cords and spring mechanisms all have a working load, and a big blind is heavy. Ranges set their maximums well inside the point where operation becomes a struggle or a safety problem.
Why the maximum differs by blind type
Different engineering means different ceilings. As a rule of thumb the ordering runs: vertical blinds typically span the widest, roller blinds commonly come next, and roman blinds are usually narrower again, because a roman lifts its entire fabric weight in folds on cords. Wooden venetians often sit towards the narrow end too, since timber slats weigh a lot. Treat that ordering as a pattern rather than a promise: the actual figures vary between ranges, between mechanisms and even between fabrics in the same range, so always check the range's own limits before you order.
Drops are limited too
Width gets the attention, but the drop has a ceiling as well. A longer drop means more fabric wound onto a roller tube, and the roll fattens until it can foul the cassette or brackets. On romans and venetians, a longer drop is simply more weight to lift. Some ranges also cap the total area, so a blind can pass both limits separately and still be refused as a whole.
There are minimums as well
Less well known is the other end of the scale. The mechanism has to live somewhere: brackets, control ends and a chain or motor all need room before there is any fabric, so every range has a minimum width and drop below which the blind cannot be built. Tiny cloakroom windows and slim side panes can come in under the minimum, so check the small end of the limits too before you fall for a fabric.
What to do when your window is over the limit
- Split the opening across two or three blinds, butted edge to edge on one window. It is the standard answer for very wide glass, and it works, but be honest with yourself about the join: there will be a slim vertical line where the blinds meet, and a little light will find it. Keeping the blinds identical and raising them to the same height makes the join read as intentional.
- Switch type. If a roller or roman cannot span the opening, a vertical very often can, precisely because of how its weight is carried.
- Look for ranges built for wide spans. Some are engineered specifically for large glazing, with stiffer tubes and heavier-duty rails, and publish larger maximums accordingly.
Motorisation can raise the ceiling
On some ranges the motorised version of a blind comes in larger sizes than the manual one, because a motor can lift a weight that would be unreasonable to haul on a chain or cord. If your opening sits just past a manual limit, it is worth checking whether the same blind with a motor stretches further. The reverse applies at the small end, where a very narrow blind may lack room for a motor at all.
The short version: size limits are physics plus honesty, not shops being awkward. Measure the opening first, then check the range's own limits, biggest and smallest, before you set your heart on anything.
Frequently asked questions
Why do blinds have maximum sizes?
Fabric comes on rolls of a fixed width, long roller tubes bow in the middle, and headrails and lifting mechanisms can only carry so much weight. Each range sets limits well inside what its parts can manage.
Which type of blind can be made the widest?
Vertical blinds typically span the widest openings because the weight hangs in separate louvres along the track. Rollers commonly come next, with romans usually narrower still. Always check the range's own limits.
What can I do if my window is wider than the maximum?
Fit two or three matching blinds side by side across the opening, switch to a vertical, or look for a range engineered for wide spans. Expect a slim line of light where two blinds meet.
Do blinds have a minimum size too?
Yes. Brackets, control ends and the mechanism need room before there is any fabric, so every range has a minimum width and drop. Very small cloakroom windows can fall below it.
Are drops limited as well as widths?
Yes. A longer drop adds fabric and weight, so drops have maximums just as widths do, and some ranges also cap the total area of the blind.
Does motorisation change the size limits?
Sometimes. A motor can lift weight that would be hard work on a chain or cord, so some ranges offer their motorised blinds in larger sizes than the manual version. Check the specific range.