I knit the same sock, over and over again, in different yarns. I've memorized the pattern, so that the only calculation I need to do is figure out how many stitches to cast on in the beginning. The rest of the pattern can be derived and measured as you go.
If you would like to add individual toes to your socks, see my toe calculator.
First, determine your gauge by knitting a test swatch on at least 20 stitches. Multiply your gauge by the circumference of your foot to determine the number of stitches to cast on. For example, if I'm getting 9 sts/in and my foot is 8" around, then I'll cast on 9 x 8 = 72 stitches.
Cast on one quarter of the stitches on each of four double-point needles. In my example, I'd cast on 18 sts per needle.
Work K1P1 ribbing around for 3" or until desired length for ribbed portion of cuff. Switch to stockinette and work another 3" or until cuff measures desired length. Finish at the end of a round (use the cast-on tail to figure out where that is).
Knit across one dpn. Then turn the work and purl across two dpns. The stitches on these two dpns will form the heel flap. I usually put all heel sts on a single dpn for this part.
Next, make the heel flap: *sl1, k1* to end, turn knitting around, slip the first stitch, p to end. Repeat these two rows until heel flap measures desired length (mine is 2 1/8"). End on a wrong-side row.
Knit across half the heel flap stitches. K2, SSK, K1. Turn (yes, you're in the middle of the row). P5, P2tog, P1. Turn (yes, still in the middle of the row).
Now, knit across until you see the last stich you knit before turning -- there will be a gap between it and the next stitch. K2tog using this stitch and the one after it. K1, turn. Purl across until you see the last purl stitch before the gap. P2tog using that stitch and the following one, P1, turn. Repeat these two rows until you have consumed all the stitches on each side and you are working your K2tog/P2tog's at the end of the row. End with a right-side row.
With RS facing, pick up and knit one stich every other row. The slipped edge stitches on the heel flap should make this really easy: insert the needle under those two loops along the edge. You should be picking up approximately as many stitches as you cast on to one dpn originally.
Knit across the two dpns that were holding the instep stitches while you knit the heel flap. Pick up the same number of stitches along the other side of the heel flap.
(Sometimes I'll forego the final P2tog row while turning the heel, and use it as one of the picked up stitches in this step.)
Count how many stitches you have on the turned heel. Knit half of these on to the same needle you used to pick up the left side of the heel flap. Slip the remainder onto the next needle. Knit one round, twisting the picked-up heel flap stitches to prevent them from making holes (i.e., k1b).
Starting from the bottom of the heel, knit to 3 sts before end of first needle. K2tog, K1. Work across the next two needles, K1, SSK, K to end. You should be back to the bottom of the heel. Knit one round even.
Repeat these two rows until you have the same number of stitches on each of the needles. This should be the same number you cast on originally. Knit around and around until the foot measures 2" less than the desired foot length.
I knit a round toe because I like to have more room for my toes. Starting from the bottom of the heel, K to 3 sts before the end of the first needle, K2tog, K1. On the second needle, K1, SSK, K to end. On the third needle, K to 3 sts before the end, K2tog, K1. On the fourth needle, K1, SSK, K to end. This is a decrease round.
The round toe is shaped as follows: decrease round, 3 rounds even, dec rnd, 2 rnds, dec rnd, 2 rnds, dec rnd, 1 rnd, dec rnd, 1 rnd, dec rnd, 1 rnd, dec. The pattern is this: 3-2-2-1-1-1. After the shaping rounds, work decrease rounds until 5 sts per needle remain.
Use Kitchener stitch to graft the toe closed.