Roman blinds maintain their role as one of the most elegant window treatments available today. Unfolded, they cover the window in one long sheet of fabric. When raised, the Roman blind accordions onto itself, resulting in a graceful arrangement of horizontal folds of drapery fabric. To make your own Roman blinds you must calculate carefully to achieve a good fit. One of the most important calculations is the stacking height, or stackage, which is the length of the blinds when pulled all the way up.
Determine your desired mounting location for your Roman blinds: inside or outside the window frame. While most people think of inside mounted blinds when they consider Roman blinds, outside mounted blinds have the advantage of not blocking as much of the natural sunlight coming through the window when the blinds are pulled up.
Decide how much of the window you want to show when the blinds are up. If the windows are very tall, you're using an outside mount, or if your blinds will be ornamental, you may want to show more of them, up to 45 cm (18 inches). Smaller windows, blinds with inside mounts, and darker rooms that benefit from as much natural light as possible should consider smaller stackages, no more than 20 to 30 (8 to 12 inches).
Measure the height of the window to determine the total length of your blinds. Remember to measure outside of the window frame if you plan on an outside mount, and from the top to the bottom of the window for an inside mount.
Calculate the height of the individual Roman blind folds as follows: subtract the stackage height from the total blind length. Subtract an additional 20 cm (8 inches) for the lowest portion of the shade, which falls behind the rest of the folds. Divide this number by the number of flaps you desire, approximately 4 to 8. This will give you the total length of each flap of the blinds. Each flap is made up of 2 folded segments. Divide this number by 2 to get the height of each individual fold. For example, if your total shade length is 150 cm (60 inches), your desired stackage is 30 cm (12 inches), and you want 4 flaps, your fold height will be 12.5 cm (5 inches).
You may find it useful to hold up a strip of fabric at the top of your window to help in determine your desired stackage height. This calculation does not show the amount of fabric needed to make the blinds. Additional considerations, such as what type of pulley is used, must be considered when purchasing fabric.