with any yarn... just keep knitting until you like the size.
I simply choose a yarn and then choose an appropriate needle size for
that yarn (circular needles as the shawl does get quite long on the needle).
I would use a larger rather than smaller needle, if you have to choose, for a better drape.
Cast on 3 stitches.
Knit 6 rows.
At the end of the last row, do not turn your knitting over, but, instead, rotate what you have done 90 degrees clockwise. Pick up and knit 3 stitches along this long side of the rectangle, using the garter stitch ridge. Turn another 90 degrees clockwise and pick up another 3 stitches from your cast-on edge. Now you have 9 stitches on your needle.
Turn your work over and knit across all nine stitches, stopping before and after the middle stitch to place a stitch marker on either side of that middle stitch.
Work the rest of the shawl as follows:
(Right Side): K2, M1L, K to first marker, M1L, slip marker, K1, slip marker, M1R, Knit to last two stitches and M1R, K2
(Wrong Side): K2, M1L, K to first marker, slip marker, K1, slip marker, K to last two stitches, M1R,
Work these two rows repeatedly until shawl is the size you wish it to be.
Bind off in what ever loose
manner you like.