On a made-to-measure order form, one field outranks every other: the choice between recess size and exact size. You can measure to the millimetre and the blind will still arrive wrong if this option is set incorrectly, because the two settings tell the maker to do opposite things with the very same numbers.
Recess size: you give the opening, they make the deduction
Most windows sit in a recess, the opening in the wall around the glass. Choosing recess size says: these figures are the size of that opening, and the blind is going inside it. The maker then deducts a small clearance from the width, and often a little from the drop, so the finished blind hangs inside the recess without scraping the plaster or jamming against the sides, with room for the brackets as well.
The crucial point is that the deduction is the maker's job, not yours. How much comes off varies by blind type and from shop to shop, so never assume the amount and never take it off yourself. Give the full opening size, untouched, and let them do the arithmetic the blind was designed around.
Exact size: the blind is made to the number
Exact size means precisely that: the blind is manufactured to the stated width and drop with nothing taken off. It is the right choice when the blind hangs outside the recess, fixed to the wall or the frame above the opening, where you want the blind bigger than the hole it covers so it overlaps on every side and blocks the light around the edges. With exact size the thinking is yours: measure the opening, add the overlap the measuring guide recommends, and type the finished figure.
The two classic mistakes
- Deducting your own clearance, then choosing recess size. You measure the opening, knock a bit off to be safe and enter the reduced figure as a recess size. The maker deducts again, and the blind arrives doubly small, with a strip of light down each side. If you choose recess size, the number you enter must be the true opening.
- Entering the recess size for a blind fitted outside. The blind is going on the wall, but you give the size of the opening. At best it matches the hole edge to edge; at worst it is smaller still after deductions. Either way it cannot overlap, so light leaks around all four sides. Outside the recess, choose exact size and include the overlap.
Decide the fit first, then measure
The order of operations matters. Before the tape measure comes out, decide where the blind will live: inside the recess, or outside on the wall. Inside looks tidier and keeps the sill usable, but the recess needs enough depth for the brackets, and the blind must clear window handles as it moves. If the recess is shallow, or handles stick out, fit outside. Once the fit is decided, the size option chooses itself: inside means recess size, outside means exact size. Then measure the way the retailer's own guide describes, because guides differ on the details and the deduction applied is theirs alone.
Measure in three places, use the smallest
Window openings are rarely square. For a recess fit, measure the width at the top, the middle and the bottom, and use the smallest of the three, so the blind clears the narrowest point rather than wedging at it. Do the same for the drop on the left, in the centre and on the right, and again keep the smallest. For an exact-size blind outside the recess, measure the opening and then add the recommended overlap to each edge instead.
Keep a note of what you entered
Write down your measurements, the figures you typed and which option you selected. If a blind arrives narrower than the opening and you ordered by recess size, that is usually the deduction doing its job rather than a fault, so check the difference against the maker's stated allowance before reporting it. And if you spot a mistake after ordering, contact the shop at once: a made-to-measure blind can often be changed before it enters production, and rarely after.
One field, two meanings: recess size hands the maker your opening and the responsibility for clearance; exact size hands you the number and the responsibility for overlap. Decide the fit, pick the matching option, and the rest of the form takes care of itself.
Frequently asked questions
What is a recess measurement?
It is the size of the window opening itself. You give the full opening figures, and the maker deducts a small clearance so the finished blind fits inside without catching the sides.
What is an exact measurement?
The blind is made to precisely the width and drop you state, with nothing taken off. It is used for blinds fitted outside the recess, where the blind should overlap the opening.
Should I deduct the clearance myself for a recess blind?
No. Enter the true opening size and let the maker deduct. If you take some off first, the blind is reduced twice and arrives too small, with light gaps at the sides.
How much is deducted from a recess size?
It varies by blind type and from shop to shop, so never assume a figure. Check the range's measuring guide or ordering page, and ask before ordering if it is not stated.
Why measure the width in three places?
Openings are rarely perfectly square. Measuring at the top, middle and bottom and using the smallest figure means the blind clears the narrowest point of the recess.
My blind arrived narrower than the size I gave. Is it faulty?
Not necessarily. If you ordered by recess size, the maker deducts clearance on purpose, so compare the difference against their stated allowance before reporting a fault.