Project planning and calculations

I made a thing to do the maths for me.

Keep a copy of the calculations you do, and update it after you’ve finished your project to note if something was different to you expected, for example shrinkage was higher than you expected.

First work out what the finished dimensions of your cloth should be. You’ll need to weave a thing that is wider and longer than this. You get draw-in when you weave, so the width is less than it is on your loom, on average 10%. Your weft is under tension so you get take-up, so make your warp little bit longer than it would be when you take the cloth off the loom at the end. Yarns are likely to shrink a bit in all directions when you wash/finish them.

Use a WPI tool, or a ruler, to ask your yarn what its natural sett looks like. This tells you how many threads can sit closely together under tension. To get a balanced weave, you want to halve your WPI to get a number for ends per inch. Multiply this out with your desired width, so you know how many warp threads you need.

If you want fringe or other decorative edging, or spare cloth to do a hem, you’ll need to add this into your warp length too - remember to calculate for both ends! Add this to your desired finished length and your take-up to get the warp needed for one instance of the thing you want to make. If you want to warp for >1 of the thing, you can multiply out this measurement now. Then add in the extra length for loom waste, you only need to do this once per warp, not per item you’re making. You probably want to round your warp number to the nearest half-yard.

Work out the total yardage you need for the warp by multiplying the total number of ends you have by the warp length. Remember that yardage on a ball band can vary by 10%, so err on the side of buying a second ball if you are close.

For weft yardage, start by working out how much yarn you need per woven inch, so picks per inch times the width in reed. Then multiply that by the desired finished length (plus take-up, but not including fringe/hem), and convert to yardage. Usually you need a fair bit less yardage for weft than warp.