Weaving Math
I have an Ashford Rigid Heddle Loom and get ridiculously tired of calculating how much yarn I need for a project every time I want to start one. I kept writing things down on post its, or in notebooks, and losing them. It was such a slow process, that I decided I needed to streamline it. So here it is, streamlined. I’ve done a ton of math and put together a spreadsheet with information on yardage requirements, width, and length. The links are the bottom of this post and jumbled in the text below.
Since I put quite a bit of time and effort into creating the spreadsheet, I thought it would be a good idea to share it with other people who may be having the same struggles.
Before you view the spreadsheet, there are a few things you need to understand first about the weft estimates made.
- The assumed warp length is always 9 feet (3 yards).
- The calculations are not exact, they are meant to serve as guidelines. Often times, these calculations are generous. I feel it’s better to be safe than sorry.
- I have not accounted for shrinkage, fiber content, loom waste, etc. There were too many variables to attach, so I didn’t use them.
- I would recommend the following additional calculations for less stretchy fabrics: 18 inches for loom waste, 10% shrinkage. For wool/nylon sock blends, you may want to account for additional shrinkage.
- These calculations are for a rigid heddle loom. I can’t guarantee that they will work with a table or floor loom.
- The reed sizes are the Ashford sizes.
- The method of calculation I’m using is one I was taught from a friend. I do not know if it is the best way to calculate weft lengths, but it works for me, despite being a little generous. If you have another method that works for you, I’d recommend sticking to it. If you’re looking for a new method, give my chart a try.
- The yardage amounts used are based on my personal yarn preferences.
Now that we have that out of the way, let’s talk about how to read the Weft Math spreadsheet (click there to see it). I abbreviated a lot of the column headers, so I’ll go through them from left to right.
Reed: this column contains the information for the reed size and yarn. The information is listed once for each set of data.
Width: desired width of the project, in inches.
Warp: amount of yarn needed to achieve a 3 yard (9 foot) long warp in the length stated in the previous column. For the number of ends needed, see this sheet.
WPI: the wraps per inch for the particular yarn. Please note, the ones I have used are standard, with the exception of the data set regarding Plucky and Sundara fingering weight yarn.
Assumed yards: the amount of yarn assumed by this data set that you have for the weft only. The information for “Assumed yards” does not take into account the amount needed for the warp.
In/yd: this column exists for formula purposes within the spreadsheet. 36 inches/yard.
Total ins: this is used to help calculate the amount of yarn needed. It represents the inches of yarn you have available.
Rows: the number of rows that can be achieved using the selected yarn. This is calculated by dividing the total number of inches by the number of WPIs.
Inches: how many inches long your project will be. This is calculated by dividing the number of rows by the width.
Feet: how many feet long your project will be. This is calculated by converting from inches to feet. This was done simply so that I would be able to understand larger numbers. I have no idea have many feet 2,000 inches is!
Yds needed: how many yards you would need to complete a project of the size listed in this column. The size listed in the column can be found by consulting the “width” and unhighlighted “feet” columns. Obviously this is not practical for some projects (who needs a 24 foot long anything?), but it is helpful when you get to the more middle ranges for those looking to complete a specific size. (Remember, this chart calculated warp math for a 9 foot [3 yard] warp. If your finished size is significantly longer than 7 feet, you will need to remember to make a longer warp, which requires additional yardage. You obviously cannot make a 24 foot long scarf from a 9 foot warp.)
Now we are on the last 4 columns, all of which have the headers highlighted in green. These columns give you information about the size of your project if you take into account the warp and the number of yards available to you after warping the loom. These columns are much more practical for those interested in creating one (or two) skein projects. By using the information in the green columns, you will be able to determine the maximum width and length available to you from one (or two) skein(s) of yarn. Genius, no?
Yds avail: the number of yards available when you take the warp into account. If there is no data in the column, you cannot complete the project using only the assumed yardage. Basically, you subtract the yards used for the warp from the total yards available. Example: if you have 450 yards total (“Assumed yards” column) and use 150 for the warp (“Warp” column), this column would read 300.
Available ins: the total number of inches of yarn available after subtracting the amount used for the warp. This is caculated by converting the “Yds avail” column into inches.
Rows: same idea as the previous “Rows” column.
Inches: same idea as the previous “Inches” column.
Feet: same idea as the previous “Feet” column.
So there you have it! Weaving math. I hope this helps people out. If you have any questions or concerns, please comment and I’ll reply to you individually, or publicly on the blog.
Here are the links to the sheets:
Number of ends and yarn requirements for warps.