How to Measure for Roman Blinds: Inside Recess and Outside Mount

Before You Measure

You need to decide two things before taking any measurements:

1. Mount type — inside the window recess, or outside the recess on the wall/frame
2. Drop end point — where will the bottom of the blind hang?

Get these two decisions right and the measurements are straightforward.

Inside Recess Measurement

An inside recess mount sits within the window frame. The blind fills the recess opening.

What to measure:

• Width: The inside width of the recess at three points — top, middle, and bottom. Use the smallest measurement.
• Drop: From the top of the recess to where you want the blind to end. Usually the full recess depth (to the windowsill) or to a radiator below the sill.

What the calculator does with these measurements:

• Deducts 2 cm (0.8”) from your width for clearance — without clearance the blind binds on the recess sides
• Uses your drop measurement as the finished drop

Tip: Measure in three places because window recesses are often not perfectly square — walls settle, frames move. Using the smallest width prevents the blind from being too wide to hang.

Outside Mount Measurement

An outside mount sits on the wall above the window, wider than the window frame. This is the most common professional installation method.

What to measure:

• Width: The width of the window frame (or the area you want the blind to cover)
• Drop: From the point where the batten will be fixed (on the wall, above the frame) to where the blind ends

What the calculator does with these measurements:

• Adds 10 cm (4”) to your width for side overlap (5 cm / 2” each side)
• Uses your drop measurement as the finished drop

How much to extend beyond the window:

• Sides: 5 cm (2”) each side minimum. 8–10 cm (3–4”) recommended for better light blockage.
• Above: Mount the batten 10–15 cm (4–6”) above the top of the window to make the window appear taller. The batten height is separate from your drop measurement.
• Below: For sill-length: end 1–2 cm (0.5”) below the sill. For floor-length: 1–2 cm above the floor.

Measuring Drop (Both Mount Types)

The drop (finished length) is measured differently depending on the bottom reference point:

Bold = most common practical choice for UK kitchens and sitting rooms.

Bay Windows

Bay windows have three or more angled window sections. Each section must be measured and made as a separate blind.

Steps:

1. Measure each section individually at width and drop
2. Note the angle of each section — corner sections may need angled battens
3. Calculate each blind separately using the Roman Blind Calculator
4. If using matching fabric, order all fabric at once to ensure dye lot consistency

Corner fitting: Corner sections in a bay need a specially cut batten to follow the angle of the wall. The fabric itself is cut and made the same way — only the batten is different.

Recess Depth Check

Before choosing inside recess mount, check the recess depth (how far the window sits back from the wall face).

If the recess is too shallow, the blind will protrude into the room or not stack cleanly. Use outside mount instead.

Common Measuring Mistakes

Measuring the glass, not the recess: The glass is always smaller than the recess. Measure the full recess opening, not just the glass area.

Ignoring window handles and locks: Check for projecting handles on casement windows. The blind must clear them when operated. Add 5–10 cm below the handle or use outside mount.

Measuring only once: Always measure width in three places (top, middle, bottom) and use the smallest. Old houses especially have uneven openings.

Not accounting for the batten: The batten sits above the blind. Add batten height (typically 5 cm / 2”) to your drop if you want the fully lowered blind to reach a specific point.

Use the Roman Blind Calculator with your measurements to get cut fabric dimensions and fold count.

See also: Roman Blind Fabric Formula and How to Calculate Roman Blind Folds.