A friend of mine from Berkeley, where summers are frigid, asked me if I could knit her a pair of Japanese split-toe socks (Tabi) to wear with her Birkenstocks. I didn't really know but figured it should be possible. Luckily I had an unfinished sock that was just her size, with 60 stitches in a 4-ply sock yearn, knit on 2mm needles. I used magic loop. So I decided to use it as a test case and as a model for the "real" socks out of the yarn she chose at a local store.
I found guidance on the "Camy's Loft" blog:
But I didn't really like the very squared-off edge on the larger side of the split, next to the big toe.
So - here is my "formula," with thanks to Cami as well:
Do your favorite cuff-down sock. When you get to the point where the toe splits, use her formula of total number of stitches divided by 6. For these socks, which had 60 stitches, that meant a result of 10.
So, I took 10 stitches from both the instep and the sole (what she refers to as the "heel") for a total of 20 stitches, and remove the rest of the stitches onto a separate needle or a piece of cotton string. Then I added another 10 stitches by knitting them on, and close the circle, making a total of 30 stitches for the big toe.
(To eliminate holes, I picked one extra stitch on either side of the bridge, and then eliminated them the next round with a psso).
Cami's guideline of 18 rows for the toe worked just fine, so I knit 18 rows, then did the decreases as she suggested - 1 row with [k2tig, k1*], the second row plain, and the third and fourth rows all k2tog. That left me with 5 stitches, which I pulled like a drawstring, then pulled into the toe and wove in.
For the rest of the toes, pick up the reserved stitches, as well as the 10 "bridge" stitches, again picking up an extra stitch on either side of the bridge to eliminate holes, and then do psso's with them on the next round, for a total of 50 stitches.
I then knitted 10 rows normally, which brought me about 1/3 of an inch before the end of her little toe. Then did the next 8 rows this way:
Row 11: knit till 3 stitches before the end of the sole on the little toe side, k2tog, k1. When continuing onto instep, k1, ssk.
Row 12: plain row
Row 13: As row 11
Row 14: plain row
Row 15: As row 11, but do a decrease on the top and bottom on the big toe side as well. *
Row 16: plain row
Row 17: As row 15
Row 18: Plain row
So we've gone from 50 to 38 stitches, or 19 on the top and 19 on the bottom.
I then did 2 rows with k2tog's and ssk's in the same way but on BOTH ends, i.e. on instep and sole on the big toe side AND the little toe side. The two decreases by the second toe are all it takes to eliminate that square edge. (If you like the square edge, don't do them.)
This left 30 stitches total, or 15 on the instep and 15 on the sole.
I then bound off with the kitchener stitch.
This worked for my friend's foot - the end of her big toe and second toe are exactly in line and there's not much of an angle on the rest or her toes. You could of course tweak it a bit to fit an individual foot, as long as you write down what you've done. My friend's left foot is about 1/3 of an inch longer than her right foot, so I'll take that into account.