How to Plan a Project: Calculating Weft

This Article is part of a series about Project Planning
Bobbins wound with hand dyed alpaca weft.
Bobbins wound with hand dyed alpaca weft.

Have you ever planned your weaving project, full of excitement to weave it off the loom? You get rolling, winding bobbins and just full of anticipation to see your finished creation? Then, about ¾ of the way through the project, you go to wind another bobbin and you can’t find your weft yarn. Why can’t you find it? Because you have used it all up because you didn’t account for the amount of weft you would need. So when you order more yarn or go to your local yarn shop, you can’t find the same dye lot, and you are left with a project which is not up to your standards.

Here is how you can prevent all of that from happening!

(This information is again sourced from the Weaver’s Companion)

Width on loom in inches = (This is information that you can find in your warp calculations)

+ 10% of that length = (the 10% will account for the take up, which is the amount of yarn used to go over and under the warp threads)

= Length of one weft shot (this is the amount needed to make one pass with your weft across the width of your project, plus the take up)

Length of one weft shot * Number of weft shots per inch = (Now this may require some sampling, which is why it is advised to add a couple extra yards to your project warp to accommodate for these tests, and also to see if your warp is at the correct sett. You can also guesstimate this information by check your ends per inch. If you are planning to weave a balanced fabric, like plain weave, you want your picks per inch to equal your ends per inch. So if your EPI is 12, you would want your PPI to also be twelve. If you are doing twills, you would want to increase your EPI and PPI by 20-30%)

= Inches of weft needed to weave one inch

An couple inches woven on loom.
An couple inches woven so that I could calculate how much weft I needed for this project.

Inches of weft needed to weave one inch * Total inches to be woven = (This is your Project Length + Fringe + Take Up + Shrinkage in your warp)

= Total inches of weft needed (The total amount of weft needed to finish your project right!)

Total inches of weft needed / 36 = Totals yards of weft needed

You DO NOT want to just buy enough weft yarn to finish your project. This is a precursor for disaster. You want to have enough for a sampler, and to accommodate some mistakes. When you buy only enough to finish your project, it means you are not giving your self enough wiggle room to make mistakes.

My army of bobbins at the ready.
My army of bobbins at the ready.

This may also eliminate over-winding your bobbins. I notoriously have bobbins filled with yarn from projects where I just got into the groove and didn't realize that I wound off way too much to finish the project. So now I have an army of bobbins- ready to be used as packing weft, something to test with, tapestry weft, or just something to weave my header. But this can be frustrating when you need a set of bobbins for your work and they are all taken up with past projects. So keep that in mind when you are calculating. I know that I am going to purchase myself a yard counter so I can wind exact yardage needed per unit in my warp to possibly eliminate this over-abundance of bobbins filled with weft.

Don’t be afraid of math! With weaving there is quite of bit of calculations going on, but it is practical math that will yield in a final product that you will be excited to show off to your friends and family, or just to weave for yourself, for your own pleasure.

I hope that was helpful! Stay tuned for more helpful advice on how to dress your loom, fix mistakes, and find your wild creative side.