Step 3: Calculate Fabric Quantity
Fabric is ordered in a length of metres cut from the roll. Before calculating fabric quantities you will need the following:
- Pole Length
- Finished Curtain Length (see Step 2)
- Fabric Width
- Vertical Pattern Repeat (if using patterned fabric)
- Fullness Ratio
- Hem allowance (20cm for full length curtains (double 10cm), 16cm for sill length (double 8cm))
- Heading allowance (5cm)
With this information we :
- Calculate the NUMBER OF WIDTHS OF FABRIC required to make the pair of curtains
- Calculate the FABRIC CUT DROP
- Then Calculate* the amount of FABRIC REQUIRED.
* Note: The final calculation depends on whether the fabric is PLAIN or has a PATTERN.
NUMBER OF FABRIC WIDTHS
To calculate the number of fabric widths required to make your curtains:
- Multiply Pole Length by Fullness Ratio.
- Divide this figure by the Fabric Width.
- Round the result up or down to the nearest whole number*.
- This whole number is the number of widths you require to make your curtains.
FABRIC CUT DROP
To calculate the Fabric Cut Drop
- Fabric Cut Drop* = Finished Curtain Length + Heading Allowance + Fabric Hem Allowance
PLAIN and PATTERNED FABRIC are treated differently at this stage
FABRIC QUANTITY REQUIRED (Plain Fabric)
To calculate the amount of plain fabric required to make a pair of curtains:
- Multiply the "Number of fabric widths" by Fabric Cut Drop.
Alternatively try our online calculator.
FABRIC QUANTITY REQUIRED (Patterned Fabric)
This tutorial is based on a normal pattern repeat fabric, if your fabric has a half drop pattern repeat please read HERE and adjust the instructions accordingly.
When the fabric has a pattern we also have to take into account that the pattern will need to line up where we join fabric and the pattern will need to be in the same position on each curtain.
To enable this we adjust the fabric cut drop so we can get a cut drop starting at the same pattern position each time.
ADJUSTED CUT DROP
To calculate the Adjusted Cut Drop:
- Divide the Fabric Cut Drop by the vertical Pattern Repeat
- Round the result up to the nearest whole number
- Multiply the whole number by the vertical Pattern Repeat
- You now have the Adjusted Cut Drop (ACD)
- The Adjusted Cut Drop is also a whole number of vertical pattern repeats, note this number down for use in measuring cut drops in step 6.
FABRIC QTY
To calculate the amount of patterned fabric required to make a pair of curtains:
- Multiply the "Number of fabric widths" by Adjusted Cut Drop.
- Add one vertical pattern repeat (this allows you to choose where the pattern starts)
Alternatively try our online calculator.
This video explains
- The difference between half drop pattern repeat and normal pattern repeat
- Adjusted cut drop
Questions & Comments
Hi Cindy, in terms of your instructions above, do I treat a fabric like this with a decorative vertical design as plain or patterned? Thanks S
You treat a plain vertical stripe as a plain because there is no vertical pattern repeat. The fabric you have does have a vertical pattern repeat so we would treat it as a patterned fabric . The sticker says it is 23cm height (vertical) PR. There may be a subtle difference in the pattern that is repeating every 23cm.
Your curtains are long. If you railroad your fabric, you will have unsightly join across the width. I am not sure what you would gain and the curtains would not look good. Railroading would only work for curtains if they are short - not longer than 1 width of fabric including tops and turns.
If I have understood your question correctly, absolutely do not railroad your fabric.
Good luck with your project. Cindy
Your curtains are long. If you railroad your fabric you will have an unsightly join across the width. I am not sure what you would gain and the curtains would not look good. Railroading would only work for curtains if they are short - not longer than 1 width of fabric including hem and heading allowance. If I have understood your question correctly I would absolutely not railroad the fabric.
Good luck with your project Cindy
Hi Cindy.
Thank you for your advice regarding railroading fabric.I can see what you mean and will not do it.
Hi. I have calculated my fabric widths, but I can’t see where it tells you how many cms to use in the joining - For my fabric, lining and interlining? I have added on the 10.5 per curtain for the ease and overlap, but can’t see that this includes the joining on the panels.
The small amount of fabric you use for joining is effectively included in the fullness ratio figure which ensures you will have made a wide enough panel to pleat up.