# Calculating weft yarn quantity

Once you have decided on a project you may want to work out how much yarn you are going to need. This may be so you can buy or dye the correct amount without vastly over or under estimating.

The following will take you through the calculation to work out how much weft yarn will be needed. It looks like a lot but they should be relatively straight forward things to work out. For the sake of simplicity I will work in centimetres/meters but the same can be applied to inches/yards.

The calculaion is as follows:

Total number of picks x total width of fabric (m) = amount of yarn needed (m)

How to work out the total number of picks

• PPC (picks per cm) x (length of woven piece (cm) + shrinkage/take-up (cm)) = Total number of picks
• The picks per cm is usually determined by sampling but if it has no been woven before see CALCULATING A SETT and use the same as the epc.
• The shrinkage/take-up is usually assumed to be 10% of the width of the woven piece but this can vary by a large amount depending on the yarn, structure and finishing. Sampling will give you a more accurate number.

How to work out the total width of the warp

• width of woven piece (m)+ shrinkage/take-up (m) = Total widthof warp (m)
• The shrinkage/take-up is usually assumed to be 10% of the width of the woven piece but this can vary by a large amount depending on the yarn, structure and finishing. Sampling will give you a more accurate number.
• It is often easier to work out the calculations in cm and then convert to m by dividing by 100 at the end.

As a working example:

Total number of picks:

• 8 ppcm
• 200cm length of woven piece
• 10% of 200cm = 20cm shrinkage/take-up

8 x (200 + 20) = 1760 picks

Total width of warp:

• 50cm wide woven sample
• 10% of 50 = 5cm shinkage/take-up

50 + 5 = 55cm (0.55m)

1760 x 0.55 = 968m of yarn needed for the warp