Measuring for curtains: rod width, stack, height, length and fullness

Open curtains take wall space, so the rod runs past the window by the width of the stack. This chapter measures the opening, the wall and the drop, chooses a fullness, and works out the rod, the panels and the finished length.

What to measure at a curtain window Understand

Blinds and shades are ordered for an inside mount, inside the window frame, or an outside mount, on the trim or the wall with an overlap past the opening; Measuring for blinds and shades covers both. The curtains in this chapter hang from a rod or a track on the wall or the ceiling, outside the frame, so they are measured from the wall around the window rather than from inside it.

That changes what matters. A shade has to fit an opening. A curtain has to cover the opening when it is closed and get out of the way when it is open, and the second job is where most measuring goes wrong. Open curtains take up wall space beside the window. If that space is not there, the open curtains cover part of the glass.

Six measurements

Use a steel tape, and write each figure to the nearest 1/8 in, as the blind makers ask. The trim or casing is the flat molding round the window. These measurements go in the window survey, which has a column for each.

Measure the floor at both ends because floors are rarely level across a wide window. SelectBlinds' drapery measuring page says that for uneven floors you measure each side and order the longest measurement. Product-specific The Shade Store's drapery guide adds that nearly all floors are not perfectly level, and plans for it with a small break or puddle, covered under Rod height and finished length.

If a rod is already up and you mean to keep it, SelectBlinds says to measure between the finials (the decorative ends). Otherwise you are about to choose the rod width, and that is the subject of the next section.

Stackback and the rod width

Stackback (or stack) is the width the curtains take up when they are drawn fully open: the folded fabric bunched at the side of the window. A pair of curtains that opens from the middle (a two-way draw, or split draw) stacks half at each side. A single curtain that opens to one side (a one-way draw) stacks all on that side. Physical principle

If the rod ends at the edge of the trim, the stack sits over the glass, and an open curtain still blocks part of the view and the daylight. To clear the glass, the rod has to extend past the trim by about as much as the stack on that side. That is the whole calculation: the rod width is the opening plus an extension each side, and the extension is the stack.

The rule we use: a third of the rod width

A Michigan State University extension bulletin, How to Make Curtains and Draperies (E-1170, 1977), says the stack space will be about one third of the fabric width, more for heavy fabrics and less for light ones, and that the rod length has to be planned for it. The bulletin is historical (the archive copy is marked as not for current recommendations); we cite it for the convention, which has not changed. Convention

The bulletin does not say whether "fabric width" means the flat fabric or the finished curtain. We read it as the finished width, about the width of the rod, because that reading matches a maker's current chart: Kirsch's 2024 stack guide gives about 14 in a side for a 96 in two-way track at double fullness, and a third of 96 in is 32 in in all, 16 in a side. Read as flat fabric, the same rod would stack 64 in, which no chart we found supports. So the rule here is: the stack is about one third of the rod width, in all, split between the sides on a two-way draw. Convention

The stack depends on the rod width, and the rod width depends on the stack. Solved together:

• rod width = opening + one third of the rod width, so rod width = 1 1/2 times the opening;
• on a two-way draw, each extension = one quarter of the opening.

For a window 48 in across the trim, the rod is 72 in and extends 12 in past the trim each side. A third of 72 in is 24 in, which is 12 in a side, so the stack parks on the 12 in of wall the extension gives it. For a one-way draw, the rod width comes out the same, 1 1/2 times the opening, with the whole extension (a third of the rod) on the stacking side.

The curtain rod, panels and length box uses this rule by default, says on the page that it is our reading of the 1977 wording, and gives two other choices: the Kirsch chart for your fullness, interpolated by track width, and your own extension each side. It then shows the stack each side and whether it clears the opening under the rule you chose.

When the wall is short

Compare each extension with the wall space you measured on that side. If the extension fits, the rod can be that wide. If it does not, there are three honest answers:

• Accept some glass covered. Extend as far as the wall allows; the stack will sit partly over the glass by the difference.
• Draw it one way. If one side has room and the other is a corner, a one-way draw puts the whole stack on the side with room.
• Use less fabric, or a different kind. Lower fullness and lighter fabric stack narrower, as the bulletin notes. A shade inside the frame, with stationary side panels, takes no wall space to open; Curtains, shades, blinds and shutters compares the kinds.

Makers' ordering pages often give a simpler figure for the extension. SelectBlinds suggests adding 4 to 8 in each side of the window; The Shade Store's drapery guide suggests 6 to 12 in each side where possible, to keep as much daylight as possible with the curtains open. Product-specific On a narrow window those figures and the one-third rule land close together. On a wide window the rule asks for more, because the stack grows with the width; a fixed 6 in leaves the stack of a wide pair over the glass.

Fullness, returns, overlap and the flat width

Fullness, stated as a multiple

Fullness is how much wider the flat fabric is than the width the curtain covers when it is closed. A curtain at 2 times fullness (written 2x) uses fabric twice as wide as the space it covers; the extra is what forms the folds. We state fullness as a multiple throughout, because the trade also uses percentages and they count differently: KnollTextiles' drapery guide (2012) defines 0 percent fullness as enough fabric to cover the opening and 100 percent as double, so 100 percent there means 2x. Convention

The usual starting point is about double. The figures vary by fabric and by heading:

The heading (the way the top of the curtain is made and hung) affects the choice. Headings that glide for daily use, such as pinch pleats and ripplefold, are made to a set fullness by the maker; panels that stay put, such as grommet or rod-pocket panels, can be fuller or plainer by choice. Style and proportion explains the headings and which suits a curtain that is opened every day. Preference Within the ranges above, more fullness looks richer and stacks wider; less fullness stacks narrower and uses less fabric.

Returns and the center overlap

Two more pieces of fabric are added to the rod width before fullness is applied.

• A return is the part of the curtain that turns from the front of the rod back to the wall at each end. It closes the side, so light and drafts do not come round the end of the rod. The Shade Store's standard return is 4 in on all its drapery except rod pocket and cubicle curtains. The depth of a return matches the rod's projection, its distance from the wall. Product-specific
• The center overlap is where a two-way pair crosses at the middle when closed, so no gap shows. Kirsch's Superfine traverse rod instructions allow 5 in for it. The 1977 bulletin, by a different method, adds 6 in to each half for overlap and rod. Product-specific

Where darkness matters, the returns do real work. The 1977 bulletin added 1/2 to 1 in to the returns to stop light at the sides. Light gaps and the stack covers the same problem for shades. Convention

The flat width

The flat width is the total width of fabric, before any folds, that the curtains need:

flat width = (rod width + 2 returns + center overlap) times fullness

For a one-way draw there is no center overlap. For a window 48 in across the trim, with a 72 in rod, 4 in returns, a 5 in overlap and 2x fullness: (72 + 8 + 5) times 2 = 170 in of flat fabric, or 85 in for each curtain of the pair. The curtain rod, panels and length box does this sum with the returns and overlap set to 4 in and 5 in unless you change them.

From flat width to what you buy

How you use the flat width depends on how you are getting the curtains:

• Ready-made panels. Divide the flat width by the width of one panel as printed on the package, and round up. Read the package carefully: some sell a single panel and some a pair, so check whether the width printed is for one panel. The box takes an optional panel width and gives the number of panels. Check the package
• Custom drapery. Many workrooms ask for the width the curtains are to cover and apply the fullness themselves. The Shade Store's guide says its ordering width is the coverage width, with fullness already accounted for, and that its workroom adds the overlaps and returns. SelectBlinds says to order the total width for a split draw and it divides it into two panels. Multiplying by fullness yourself and then ordering that figure would double the fabric. Follow the maker's order form. Product-specific
• Curtains you sew. The flat width becomes a number of fabric widths, with seam and hem allowances; the fabric for making curtains box and the making section of Buying, ordering or making take it from here.

Rod height and finished length

Rod height

Decide the rod height before you measure the length, because the length is measured from it. SelectBlinds suggests a rod 4 to 12 in above the top of the window, not counting tabs or rings, and for grommet curtains says to keep the top of the rod at least 1 in below the ceiling so the fabric above the grommets has room. Product-specific Within that range the choice is about proportion and the space you have, and Style and proportion sets it with tape on the wall before you buy anything. Write the height above the floor in the window survey, measured to the top of the rod.

Ring and clip drop

Rings, clips and eyelets lower the curtain below the rod. SelectBlinds says an eyelet with a clip adds 3 in of length and an eyelet alone adds 2 in, and that you deduct that from the panel length. A grommet panel is measured from the top of the rod; SelectBlinds measures its finished length from the upper inside of the grommet. Product-specific Hold one ring or clip of the kind you will use against the tape and measure it if you can; it is the figure that applies to your hardware. Test it

Where the hem stops

The finished length is the length of the curtain from its top (or its hanging point) to its hem. It is the rod height, less the ring drop, less any clearance above the floor, plus any break or puddle on it.

The default we use for a curtain that is opened every day is 1/2 in of clearance, which is The Shade Store's recommendation for drapery opened and closed often: the hem does not drag or catch. Product-specific Where darkness matters more than movement, a hem that touches the floor closes the gap at the bottom. The Shade Store recommends a small break or puddle for uneven floors and for natural fibers that stretch, and says linen and wool stretch; its workroom note adds that natural fibers can change a little with humidity and temperature. If your fabric is linen or wool, or your floor slopes, a break hides both. Fabric, linings and fading covers what each fiber does.

Measure the length from the rod height to the floor at both ends, and use the longer, as SelectBlinds advises for uneven floors. Then subtract the ring drop and the clearance, or add the break or puddle. A puddle on one side of a sloping floor and a break on the other is still a matched pair; a hem that clears the floor at one end and drags at the other is not.

A ready-made panel comes in fixed lengths. If none matches your finished length, either hem the panel or move the rod: raising or lowering the rod by an inch or two, within the range above, can make a stock length fit. Our practice

See it See it

• SelectBlinds, How to measure drapery: a seller's plain ordering page, with rod height, ring drop and floor finishes.
• The Shade Store, How to measure: drapery: a custom maker's guide, showing how ordering width, returns and hardware deductions work.
• Kirsch Wrought Iron 2024 Price Guide, the "Helpful Guides" pages: the pleated stack chart and the drapery weight formula.
• Michigan State extension, How to Make Curtains and Draperies (1977): the stack rule and the reasoning behind rod length, in a scanned bulletin.

Practice Practice

Minimum: one window's opening, wall space each side and floor at both ends measured, a fullness chosen, and the rod width, rod height and finished length worked out. Time: about 40 minutes. Materials: a steel tape measure, a pencil, painter's tape or sticky notes, a step stool, and one ring or clip of the kind you plan to use if you have it.

1. Measure the opening. Across the outside edges of the trim, to the nearest 1/8 in.
2. Measure the wall each side. From the edge of the trim to the nearest corner, cabinet, switch or door frame. Note anything on the wall that a stack or a bracket would hit.
3. Measure up. From the top of the trim to the ceiling, and from the floor to the top of the trim at both ends.
4. Choose a fullness. About 2x for curtains you draw daily, more for sheers. If you know the heading, read its fullness in Style and proportion.
5. Run the curtain rod, panels and length box. Enter the opening, fullness, draw, returns and overlap. Read the extension each side against your wall space. If it does not fit, try a one-way draw or a lower fullness and compare.
6. Mark the rod height with tape. Put a piece of tape on the wall at the height and at each end of the rod. Look at it from across the room and adjust before anything is drilled.
7. Work out the length. Measure from the tape to the floor at both ends, take the longer, subtract the ring drop and the clearance, or add the break. Enter it in the box.
8. Write the row in the window survey: wall space, ceiling and floor figures, and in the notes the rod width, rod height, finished length and the number of panels or the flat width.

Your windows Your windows

Check your work Check your work

Criteria

• Is the opening measured across the outside of the trim, and the wall space measured to the nearest obstruction each side?
• Does each extension fit the wall on its side, and if not, have you chosen what to do about the stack?
• Is the fullness written as a multiple, and does it suit the heading and the fabric?
• Do the returns and the center overlap appear in the flat width, and is the flat width used the way your supplier asks (panels, coverage width or fabric widths)?
• Is the finished length measured from the rod height, at both ends, with the ring drop and the floor finish accounted for?
• Are the rod width, rod height, finished length and panels or flat width in the window survey?

Worked example

The Adeyemis' row (fictional) meets most criteria. The opening is across the trim, the wall space each side is 22 in, and the 17 7/8 in extension fits it. The fullness is 2x for a curtain drawn daily. The flat width of 240 1/2 in includes 4 in returns and a 5 in overlap, and they have turned it into at least five 50 in panels. Their finished length of 82 1/2 in rests on an assumption: that the 80 in runs from the floor to the top of the trim and that the floor is level. Until they measure from the rod height to the floor at both ends, the length is potentially right and not yet checked, and that is the criterion still open.

Common mistakes

• Ending the rod at the trim. The open curtains then cover the edges of the glass. The extension is the stack.
• Applying fullness twice. A custom order form that asks for coverage width adds the fullness itself.
• Forgetting the ring drop. Rings and clips lower the curtain by 2 to 3 in at one seller; a curtain measured to the rod and hung on rings comes out that much too long.
• Measuring the length at one end. Floors slope. Measure both and use the longer.
• Measuring the length before deciding the rod height. The length is measured from the rod. Tape the height first.
• Counting panels without reading the package. Some packages are one panel, some a pair.

What is still unresolved

• Which heading, how high and how long for the look you want: Style and proportion.
• Which lining, for darkness, privacy or heat: Fabric, linings and fading.
• Whether the wall will hold the rod, and where the brackets go: Hardware and installing and the curtain weight and hardware box.
• Ordering, or the yardage for curtains you make: Buying, ordering or making and the fabric for making curtains box.
• Cords on a traverse rod where a child lives or visits: Cords, children and fire.
• How wide your own fabric stacks: hang one panel on the rod, draw it open and measure it.

Knowledge check and scenario

Checklist

• Opening, wall space each side, trim to ceiling and floor at both ends measured.
• Fullness chosen as a multiple for the heading and fabric.
• Rod width set from the stack, with the extension checked against the wall each side.
• The survey row has the rod width, rod height, finished length and the number of panels or the flat width needed.
• Stack compared under the Kirsch chart and the one-third rule, or a one-way draw considered. (Go deeper; optional)