Curtain Fabric Calculator

Rail width, cm

Curtain drop, cm

Fabric width on the roll, cm

Fullness ratio

1.5 is a light gather, 2 is standard, 3 is full.

Top and bottom allowances, cm

Pattern repeat, cm

Leave at 0 if the pattern does not need matching.

Fabric price a metre

Result

Fabric, m8.55
Cost$7,695.00
Gathered width, cm620
Cut height, cm285
Drops3
How to cut it3 drops of 285 cm

The fullness ratio decides the bill

Works out how many metres of fabric a pair of curtains needs from the rail width, the fullness ratio, the hems and the pattern repeat.

Curtains are not the width of the window. They are the width of the rail multiplied by a fullness ratio: two is the standard gather, one and a half is a light one, and three is the full theatrical look that eats fabric.

After that the question is which way the fabric runs. Wide upholstery-weight fabric is often railroaded — turned on its side so the roll width becomes the drop — and then you simply buy the gathered width in running metres. Narrower fabric has to be cut into drops and joined.

What this calculator shows

The metres of fabric needed and the cost
The gathered width and the cut height with allowances
How many drops are needed and how to cut them

What to keep in mind

Twenty centimetres are added to the gathered width for the side hems of both curtains.
A pattern repeat rounds each drop up to a whole number of repeats, which is what makes patterned fabric noticeably more expensive.

FAQs

What fullness ratio should I choose?

Two for most rooms. One and a half for a heavy fabric that gathers on its own, three for sheers and for a deliberately opulent look.

What is a pattern repeat?

The distance after which the pattern starts again. Each drop has to begin at the same point in the pattern, so every drop is rounded up to a whole number of repeats.

What allowances should be left?

Fifteen to twenty centimetres at the top for the heading tape and ten at the bottom for a hem — more if you want the option of lengthening them later.

What does railroading mean?

Turning the fabric ninety degrees so the roll width becomes the curtain drop. It removes all the seams, but only works if the fabric is wider than the drop and the pattern has no direction.

Worked example

A three-metre rail

Input: 300 cm rail, 260 cm drop, 280 cm fabric, fullness 2, 25 cm of allowances

Output: 8.55 metres

Note: The gathered width is 620 cm and the cut height 285, so the 280 cm roll cannot be railroaded and the fabric goes into three drops. Drop the fullness to 1.5 and it becomes two drops and 5.7 metres.

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Curtain Fabric Calculator

Result

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