Window treatments

How to measure for roman blinds, roller and zebra blinds: inside or outside the recess

To measure for roman blinds, first decide between inside and outside recess fitting. Inside: measure width at top, middle and bottom and drop at left, centre and right, record the smallest figures and the reveal depth. Outside: measure the recess and add an overlap on each side. Always state whether figures are recess size or made size.

Key takeaways

Decide inside or outside recess fitting before measuring, because each uses a different way of recording figures.
Inside recess: measure width and drop at three points each and record the actual recess; the maker deducts side clearance.
Outside recess: add overlap, typically at least about 5 cm per side, and label the figure as the made size.
Inside-fitted blinds always leave side light gaps; roller and zebra blinds leave wider gaps than romans because of the tube mechanism.
Corded and chain blinds need tensioners, breakaway connectors or high-mounted cleats for child safety.

Inside or outside the recess?

Inside fitting looks neat and keeps the window frame visible, but always leaves light gaps at the sides. Outside fitting controls light better and does not depend on reveal depth, but uses wall space above and around the window.

Make this decision before measuring, because the two methods differ completely. Key criteria:

Reveal depth: whether it can take the headrail, roller tube or the fabric stack when raised.
Obstructions: handles, locks and hinges of casement and awning windows.
Light control: bedrooms needing darkness favour outside fitting with overlap, or a blind layered with curtains.
Design intent: inside fitting preserves architectural lines; outside fitting makes windows read larger.

Choosing treatments by window type and room is covered in choosing window treatments by window type and brief.

How to measure a roman blind inside the recess

Measure recess width at three points (top, middle, just above the sill) and drop at three points (left, centre, right). Record all six figures, mark the smallest, and measure reveal depth.

Width: rendered reveals are rarely square. Blinds are made to the narrowest width or they will bind when raised and lowered.
Drop: from the top of the recess (or the headrail fixing line) to the sill.
Depth: from wall face to the window frame or to any protruding handle. A roman blind needs room for the headrail and for the fabric stack when raised, which is considerably deeper than the headrail.
Square: measure both diagonals; a large difference suggests switching to outside fitting.

The surveyor records the actual recess. The maker deducts side clearance, typically about 1 cm in total for roman blinds, so the blind does not rub. Label the figures clearly: recess size, no deductions.

How much to add for outside recess fitting

Measure the recess, then add overlap: typically at least about 5 cm on each side, a headrail about 5–10 cm above the top of the recess, and a bottom about 5–15 cm below the sill, or as the design requires.

More overlap means smaller side light gaps; for bedrooms, 8–10 cm each side is reasonable where wall space allows.
Check there is enough wall height above the recess for brackets and solid material to fix into, particularly near beams, gypsum pockets or cornices.
Check sill projection: a stone sill proud of the wall needs brackets with enough projection for the fabric to clear it.
For several blinds on one elevation, align headrail and bottom heights so the lines run level.

For outside fitting, the survey records the required made size and states that overlap is already included. When sending a quote request on SEAMATER, flag this per window reference so the surveyor and the workroom read the figures the same way.

How is measuring roller and zebra blinds different?

The principle is the same, but roller and zebra blinds have a tube mechanism at the top, so check depth for the tube or cassette, and expect wider side gaps than a roman blind.

Fabric narrower than overall width: brackets and the control mechanism at each end take up width, so the fabric is usually a few centimetres narrower than the overall size. Inside the recess, side light gaps are more noticeable than with romans.
Depth: the roller needs space for tube diameter plus the fabric roll; zebra blinds usually come with a front cassette. Roll diameter grows with drop and fabric thickness.
Wide openings: roller widths are limited by tube diameter and fabric. Wide aluminium sliding doors are usually split into several blinds, with splits aligned to mullions so gaps are less visible.
Zebra (dual) blinds: two layers of alternating solid and sheer stripes; light is adjusted by offsetting the stripes, never fully blacked out. Common in offices and rental apartments.

Comparison table: inside vs outside recess

How each option is measured and how the maker treats the figures. Distances are typical reference values.

Item	Inside recess	Outside recess
Width recorded	Narrowest of three recess readings	Recess plus overlap, typically at least about 5 cm each side
Drop recorded	Top of recess to sill, all three readings	Headrail position (about 5–10 cm above recess) to required bottom
Who deducts	Maker deducts side clearance	No deduction; figure is the made size
Depth check	Reveal depth vs headrail, tube, fabric stack	Bracket projection vs sill and handles
Light gaps	Yes, at sides and possibly top	Fewer, depending on overlap
Suits	Deep, square, clear reveals; design-led	Shallow reveals with handles; bedrooms

For higher light control, pair the blind with the right fabric or lining; see blackout, dimout and thermal linings.

Which control side, and how to handle cord safety?

Put the control on the accessible side, away from handles, sockets and furniture placed against the wall. Corded and chain-operated blinds need child-safety devices, particularly in family apartments, hotels and schools.

Record the control side (left or right, seen from inside) for every blind; for adjacent blinds, place controls at the outer ends so chains do not tangle.
Continuous-loop chains should have a tensioner fixed to the wall or frame.
Open cords (common on roman blinds) should have breakaway connectors and a cleat placed out of children's reach; international guidance commonly uses about 150 cm from floor as a reference.
International standards such as EN 13120 (Europe) and ANSI/WCMA A100.1 (North America) are useful references when writing the specification.
For projects with young children, cordless or tubular-motor blinds remove cords altogether; provide power at the motor end.

Notes for aluminium windows in Southeast Asian projects

Aluminium windows in apartments and townhouses in Vietnam and across the region often have shallow reveals with handles projecting inward. Outside or ceiling fitting is often more practical than inside fitting.

Measure handle projection on casement and awning windows; an inside-fitted blind must sit in front of the handle or it will catch.
On west-facing windows, strong tropical sun fades and heats fabric; consider UV-stable fabrics or screen fabrics with a suitable openness.
On coastal projects, specify corrosion-resistant components; in humid seasons, favour low-absorbency fabrics for blinds close to glass.
Log window references, photos and figures on the same survey sheet as curtains; see how to measure for curtains on site.

Once figures are fixed, site readiness and acceptance follow the installation and handover checklist. SEAMATER surveys, measures and installs roman, roller and zebra blinds; specifiers who prefer to measure themselves can use the steps above as a cross-check, on Vietnam or overseas projects. Teams can also order fabric samples inside a project and request quotes per window reference.

Frequently asked questions

How do you measure for a roman blind inside a window recess?

Measure recess width at top, middle and bottom, drop at left, centre and right, plus reveal depth and both diagonals. Record the actual recess and mark the smallest figures. The maker deducts side clearance, typically about 1 cm in total, so the blind does not rub on the reveal.

How much bigger should an outside-mount roller blind be?

Typically at least about 5 cm wider than the recess on each side, with the headrail 5–10 cm above the recess and the bottom 5–15 cm below the sill. For bedrooms needing darkness, 8–10 cm overlap each side reduces side light where wall space allows.

Do zebra blinds block light completely?

No. Zebra blinds alternate solid and sheer stripes and adjust light by offsetting them, so some light always passes, plus side gaps. They suit offices and living areas; bedrooms needing darkness are better served by blackout roller blinds fitted outside the recess or layered with curtains.

Should blinds be fitted inside aluminium window frames?

Only where the reveal is deep enough for the headrail or tube and the raised fabric, and no handles or hinges project. Many aluminium windows in the region have shallow reveals and inward handles, so outside or ceiling fitting is often the more practical option.

What is the maximum width of a roller blind?

Maximum width depends on tube diameter, fabric and control mechanism of each system, so confirm with the supplier. For wide sliding doors, the usual approach is to split into several blinds with joins aligned to mullions so gaps are less visible.

Which side should the blind control be on?

On the accessible side, away from handles, sockets and furniture against the wall. For adjacent blinds, put controls at the outer ends so chains do not tangle. Record left or right, as seen from inside the room, for each blind on the survey sheet.

Project teams can book SEAMATER to survey, measure and install roman, roller and zebra blinds.

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