When measuring for curtains, it is helpful if the hardware (poles or rods) is in place before you begin, and also carpets or any other flooring if the curtains are to be full-length. Always use a long, retractable, steel measuring tape, and ask someone to help you when measuring large windows.
Decide on the type of heading you will be making, because it can affect the location of the pole in relation to the top of the window or the trim. If you are making curtains or a shade in a fabric with a pattern repeat, place an entire pattern repeat at the lower edge, rather than the top.
Curtain width or fullness
The fabric fullness required will depend on the curtain heading. As a general rule, for each curtain in a pair, allow one-and-a-half to two-and-a-half times the width of the rod, divided by two.
Curtain length or drop
For the finished length (drop) of the curtains, measure as follows:
- For curtains hung from an exposed rod, work out where the heading will finish in relation to the rod. If you are unsure, use curtain hooks to attach a piece of heading tape to the rod, and measure down from the top of the tape.
- For curtains hung from a pole, measure the length from the bottom of the curtain ring or the eyelet.
- For curtains hung from a pole that is attached to a valance shelf (mounting board) or cornice box (pelmet box), measure the finished length from the underside of the board, then deduct the hook drop. This will depend on the type of heading and hardware you are using. If you are unsure, hook a piece of the chosen heading tape to the pole with curtain hooks. Measure the clearance between the top edge of the tape and the bottom edge of the board.
- For full-length curtains, deduct 3⁄8in (1cm) from the measurement down the right hand side of the diagram below for clearance. If you prefer curtains to puddle, or pool, on the floor, add another 6–8in (15–20cm) to this same measurement.
- For sill-length curtains, add 2–4in (5–10cm) to the measurement down the window in the diagram below, so that they hang just below the windowsill. If the sill protrudes, deduct 3⁄8in (1cm) from this same measurement, to allow the curtains to hang clear.
Estimating yardage
When making curtains, don’t skimp on the fabric yardage. Full curtains made from inexpensive fabrics look much better than ones that have been made from half the amount of a high-price fabric.
Start by calculating how many fabric widths are needed. Take your finished curtain-width (fullness) measurement and divide it by the width of your fabric. For example, for a finished curtain width of 90in (230cm) and a fabric width of 55in (139cm), you will need two widths per curtain.
If the number of fabric widths works out to be just under or over a number of full widths, round up or down to the nearest full width. If it is nearer a half width, round it up or down to the nearest half width, and place the half widths on the outer edges of the curtains when stitching them together.
Next, calculate the total yardage. Add the top and lower hem allowances (see the individual projects) to the length measurements and multiply this number by the quantity of fabric widths calculated. If your fabric has a pattern repeat, add one full pattern repeat per width of fabric, after the first width.
Where to measure
There are two main measurements needed for working out the fabric yardage:
- The length of the pole, rod (including any overlap arms at the center, if your rod has them), valance shelf or cornice box (measurement across the top of the diagram)
- The length (drop) from the curtain hardware to the floor (measurement down the right hand side of the diagram) or windowsill (measurement down the window on the diagram), depending on the style of your curtains.
Measure the finished length (drop) a few times at different points across the window, as floors can be uneven. Check whether the window is plumb (an even square or rectangle), by measuring the width at both the top and bottom. Check every measurement twice.
For more techniques, as well as beginner's projects, check out A Beginner's Guide to Making Curtains, Shades, Pillows and More by Vanessa Arbuthnott.