How to Measure Windows for Custom Drapery: A Spec Sheet
Lead With the Opening, Not the Treatment
The short answer to how to measure for custom curtains: record the window and the wall as they exist, in full, and let the treatment decisions come after. A workroom can fabricate from almost any design intent, but only if the site measurements describe reality rather than an assumption about where the rod will go.
Use a steel tape, never cloth, and measure every opening individually even when windows appear identical. In older buildings in particular, openings that read as matched pairs rarely are. Measure width at the top, middle, and bottom of the opening, and height at both sides and the center. Record the smallest and largest figures rather than averaging; the workroom needs to know the opening is out of square, and by how much.
Photograph everything. A wide shot of the full elevation, a close shot of the frame and casing, and a shot of the ceiling condition above the window answer questions before anyone has to pick up the phone.
Width: Frame, Wall, and Stackback
For width, your spec sheet should capture three things: the opening itself from inside of frame to inside of frame, the outside of the casing or trim, and the available wall space on each side of the window. That last figure is the one designers most often skip, and it is the one that determines whether panels can stack off the glass or will always cover part of the view.
Note anything that interrupts the wall plane: light switches, thermostats, vents, art, adjacent door swings, crown returns, or a corner that arrives sooner than the elevation suggests. Stackback is a design decision, but it is constrained by what the wall allows, so the workroom needs the full picture before hardware is specified.
If treatments will meet in a corner or run across multiple openings, measure the full run as a single dimension in addition to the individual windows. Cumulative measurements taken window by window drift; one continuous measurement does not.
Height: Measure to the Finished Floor, Every Time
Height is where remakes happen. Measure from the ceiling to the top of the casing, from the top of the casing to the floor, and from the ceiling straight to the floor at several points across the width of the treatment. Floors are rarely level, and a panel specified from a single height measurement will puddle at one end and float at the other.
Be explicit about what the floor is at the time of measure versus what it will be at install. If flooring, carpet, or a rug is still to come, note the finished floor condition on the spec sheet so the workroom can account for it in the finished length. Measuring to a subfloor and installing over finished stone are two different jobs.
Record the ceiling condition as well: flat, coffered, sloped, with or without crown, and whether there is blocking or structure above the window that affects where brackets can land. Mounting height drives finished length, and both drive yardage, so this is not a detail to resolve later.
The Site Conditions That Belong on Every Spec Sheet
Beyond the numbers, a complete drapery spec sheet notes the wall substrate behind the mounting points, since plaster, drywall, concrete, and steel framing each change the install plan. It notes radiators, baseboard heat, window AC units, handles, cranks, and tilt-in sashes that project into the path of a panel. It notes whether the treatment must clear an operable door, and which direction that door opens.
For motorized treatments, document power availability at the headrail location and whether the project is hardwired or battery driven, because that decision affects the hardware, the bracket detail, and sometimes the mount position itself.
At Valley Studio, our workrooms in New York and Los Angeles and our San Francisco office work from exactly this kind of sheet every day. When the site measure is complete, the fabrication conversation gets short, the install goes smoothly, and the panels break where you drew them. That is the entire point of measuring well: the craft shows up in the finished room, not in the correspondence.
Related reading: Drapery for San Francisco Bay Windows: A Trade Guide · Bracket Projection: Clearing Radiators, Trim, Romans