Sometimes curtain material suitable for smaller windows, can already be wide enough. The typical width of material is in a range from 45 - 60 ins (114.5 - 150cms) so this would mean that no joining will be needed.
Curtains for larger windows would need the fabric widths sewn together. In plain fabrics this is sometimes seen but can fall into the fold so wouldn't be duly noticed. If you were using patterned fabric you would need to buy extra fabric and join the patterns up first.
The type of track or pole used can determine the fullness of the curtain. Many of the heading tapes, such as pencil pleat look better if double width is used. This can be adjusted, if not as much gathering is wanted, to one and a half widths.
For the calculation example the window is 40
ins (100cms) wide and 40 ins (100cms) high. The curtain track extends 4
ins (10.5cms) either side of the window. A plain material was used with a width of 48ins (120cms) and the heading is a pencil pleat. The length wanted or finished length is 48ins (122cms).
This window would have been measured first to get the finished length and the finished width.
Working out the fabric widths
In this example the width of the fabric should be twice the width of the track. 40+4+4=48 ins ( window width + extra track (left) + extra track (right) = track width) or 102 + 10 + 10 = 122cms. Multiply the width by the amount of gathering you want in this case it was multiplied by 2 = 96 ins (240cms).
Then divide this by the width of the fabric in this case 48 ins (120cms)
= 2 widths. This is the amount per
curtain. A pair of curtains would need 4 widths. The pleating would be quite tight.
Track width x gathering divided by fabric width = widths per curtain. X 2 per curtain pair.
Working out the fabric length
Now that the number of widths have been calculated the next step is working out how many yards or metres to buy. Measuring the length wanted or finished length (track to hem) then adding in the heading and hem will give the Cut Length.
In the example the length wanted is 48 ins (120cms). The
amount of fabric for one drop would be 48+6+2 ins = 56 ins (finished length or length wanted + amount for heading + amount for hem or 120+15+5 =
140cms. The cut length is 56ins or 140cms.
Multiply the cut length by the total number of fabric widths. In this case 56 ins (140cms) x 4 = 224 ins (560cms) which is 6 + 1/4 yards or 5.6 metres. This can be rounded up to the nearest width so it would be 7 yards or 6 metres.
Length wanted or finished length + heading + hem = Cut length divided by number of fabric widths needed = Amount of fabric in yards or metres.
This reads more complicated than actually doing the sewing but you need to get the amount of fabric right or else you will only be making one. Which I have done in the past.
Now that the window has been measured and the amount of material has been calculated the next step is to sew the curtains.
Enjoy searching for your curtain material.