Before you start measuring your windows for curtain fabric you need to decide on a few things:
Do you have a curtain pole or track already fitted? Will the curtains hang inside or outside the window frame?
How long do you want the curtains to hang? Generally about 10cm (or 4”) below the window is normal but you may want yours to be floor length or anywhere in between the two.
How gathered do you want the curtains to be? 1.5 times gather is good for eyelet curtains, 2 times gather is about the norm but you may want 2.5 times gather which will give a very full curtain.
To measure the width simply measure the width or your pole or track if already fitted. Exclude any end finial (decorative end piece) on the pole from this measurement. If you have a track fitted measure the entire length of the track.
For the drop measure from the bottom of your curtain ring if using a pole (see pic A) or for eyelet curtains measure from the top of the eyelet where it sits on the pole (see pic B). If you have a curtain track measure from the top of the track (see pic C) to the point you want your curtains to finish, this can be either just below the window frame or to the floor or your choice of length)
To calculate fabric quantities.
As an example for a 200cm width window with a 250cm drop (finished length) with a 2x gather for normal fullness.
Multiply the finished width by the fullness you require. 200cm x 2 = 400cm
Divide this by the fabric width (20th CC fabrics are 145cm wide)
400÷145 (width of fabric) =2.75 round this up to a whole number so 3 widths of fabric will be required.
To calculate the drop take the finished length and add 25cm for hems then also add the fabric pattern repeat. Using my Starlight fabric as an example the pattern repeat is 16cm vertically.
200 (finished length) +25 (hem allowance) +16 (pattern repeat) =241.
Multiply by the amount of widths 241×3=723cm. Round this up to 7.5m
You will need 7.5m of fabric.