I spent most of my play time today measuring and sampling. First I measured the weft: I wove twenty picks in pattern, then laboriously unwove those twenty picks, measured the total length of those twenty weft shots, and divided by twenty to give the average length of a weft shot. (Which happens to be 23.25″ on a fabric that is 22.75″ at the fell, and 23.5″ in the reed. Only 2% weft take-up!)
Anyway: I then wove another 60 or so picks and used a linen tester to measure the picks per inch: about 39 to 39.5. So I needed about 23.25″ x 39.25 = 912 inches of weft to weave up one inch of fabric, measured under tension on the loom.
Armed with that information, I started knitting up sample blanks. I picked an arbitrary number of needles, started knitting, and then (after the knitting was fairly along), marked the yarn, knitted twenty rows, marked the yarn again, and knitted a couple more rows to stabilize the fabric before removing it from the machine.
Then (to mimic the dyeing process), I washed the swatch with hot soapy water and pressed it dry with a hot iron. Unraveled the swatch and measured the yarn between the marks, and divided by twenty to get the average length of one row. After five or six swatches, I determined that using 57 needles would give an average row length of 23.25″, so that forty rows (an easy number to measure) should give approximately one inch’s worth of finished weaving.
Then came the acid test: I knitted up 160 rows on the machine, using 57 needles, washed and dried the swatch, unraveled it, and wound the resulting pile of yarn onto a pirn. Wove up the sample, and…ta-daa!

As you can see, my calculations were dead on the nose: 160 rows produces just a hair over 4″ of woven fabric. I am smug. 🙂 All that tedious measurement and calculation paid off!
Anyway, after one or two more measurements, I am now armed with all the information I need to make my knitted blanks. So today and tomorrow I will be knitting up blanks to dye for the sample warps. I need three blanks, each 57 needles wide and (gulp) 2400 rows long. I’m hoping to get the first one knitted and dyed over the next day or two. That will let me get going on the first sample panel, and see how the colors blend in the weaving.
I can hardly wait! This will be really neat to play with.