Calculating plain fabric
There are a few points you need to work out first before starting your fabric calculation.

Cut drop – Firstly work out your cut drop. This is the finished drop of your curtain/blind, plus your hem and heading allowances.

Pole/Track size – Secondly what size is your pole or track? (Top tip) Where possible, have your pole or track installed before making your window dressing. This leaves no doubt over final required measurements).

Width of your fabric – You will find the width of your fabric on the information when you purchase, or you can simply measure, excluding the selvedge.

Fullness required  – For curtains, roman blinds will always be 1x fullness as you wouldn’t want any wave in a roman blind!)

Fullness guide
Pencil pleat heading tape = 2 x
Eyelets = 2/ 2.25x
Single pinch pleat =1.5 / 2x
Double pinch pleat = 2.25x
Triple pinch pleat = 2.5x
Cartridge pleat = 2.25x
Wave heading =2/ 2.25x

Now you have enough information to calculate how much fabric your window dressing requires by following these simple steps below.

Pole/ track length =……………
Multiply by fullness =………….
Divided by Fabric width =……………
Round by to the nearest full width (whole number) = amount of widths of fabric required.
Example (This is an example, you may wish to add more on for your heading allowance if you are using buckram).

Plain fabric calculation
Info : Pole/track width = 250cms Heading = Double pleat Fullness therefore is = 2.25x Fabric width = 138cms

Pole/track width 250cm x 2.25 fullness = 562.5
562.5 divided by Fabric width 138cms = 4.07 widths
Rounded up to nearest whole number = 5 widths.

Finished drop of curtain = 232cms
Cut drop of fabric = 232cms + 15cm hem allowance + 10cm heading allowance
Total cut drop of fabric = 257cms.

257cms x 5 widths = 12.8 metres of fabric Round up to the nearest whole metre = 13metres.

This pair of curtains would require 13 metres of fabric.

Calculating Patterned Fabric

To calculate how much patterned fabric you require you firstly need to work out your adjusted cut drop.
(For this example I am using the information we used above)

Fabric cut drop = 257cms
Number of widths = 5 widths
Pattern repeat on the fabric (This information should be available when you purchase the fabric. If not simply the measurement from the centre of the pattern to the next repeat of the pattern to the same point.) For this example our pattern repeat is 50cms

(Cut drop) 257cms divided by the (pattern repeat) 50cms = 5.14 round up to nearest whole number
= 6
Multiply by pattern repeat = 6 x 50cms = 300cms

300cms is your adjusted cut drop.
To now calculate how much fabric you require, multiply your adjusted cut drop by the amount of widths required = 5 widths x 300cms = 15 metres

Fabric required for this patterned pair of curtains = 15 metres