A sock is four numbers wearing wool: the cast-on (foot around, minus ease, times gauge), the heel flap (half), the turn (a short-row recipe on that half), and the toe. Enter foot and gauge; all four follow. Men’s, women’s, and kids’ sock sizes run through the same four numbers.
Foot and Gauge
Cast On
64stitches
for a 9″ foot at 32 sts/4in, 10% ease
Turn: k18, ssk, k1, turn; sl1, p5, p2tog, p1, turn, repeat, each pass one stitch wider, until every side stitch is worked. 18 heel stitches remain.
- Heel flap32 sts × 32 rows
- Heel turn beginsk18, ssk, k1; turn
- Gusset pick-up17 each side
- Start the toe at8.18 in of foot
- Graft16 and 16
The Formulas
cast on = foot around × (1 − ease) × stitches per inch, snapped to 4 · heel flap = half, worked flat for flap rows = flap stitchesheel turn: k to ⅔ − 1... the recipe the calculator writes · start the toe at foot length − toe rounds ÷ row gaugeThe square heel flap, as many rows as stitches, and the standard French turn fit most insteps; the gusset then picks up one stitch per flap ridge plus one. Toe decreases round-about-round from the full count to about a third, grafted.
Worked Example
A 9 in foot, 10 in long, at 32 sts and 44 rounds per 4 in, 10% ease:
- Cast on: 9 × 0.9 × 8 = 64.8 → 64 stitches.
- Heel: 32 stitches, 32 flap rows. Turn: k18, ssk, k1; turn: sl1, p5, p2tog, p1; turn… until the flap resolves to 18.
- Gusset: pick up 17 each side, decrease back to 64.
- Toe: begins when the foot measures 8¼ in, about 1¾ in of decreases, grafting the last 16 and 16.
Common Sock Numbers
At the classic fingering gauge, 32 sts per 4 in, 10% ease, the calculator reworks any row for your gauge.
| Foot around | Cast on | Heel flap |
|---|---|---|
| 7″ | 52 | 26 sts × 26 rows |
| 8″ | 56 | 28 sts × 28 rows |
| 9″ | 64 | 32 sts × 32 rows |
| 10″ | 72 | 36 sts × 36 rows |
| 11″ | 80 | 40 sts × 40 rows |
How to Measure a Foot
- Circumference around the ball of the foot, snug tape. The ankle usually matches near enough for a standard leg.
- Length heel to longest toe, standing. The sock knits shorter, the ease does the gripping.
- Gauge in the round: flat swatches lie about sock gauge; knit a tube swatch or start the first sock as the swatch.
Assumptions and Defaults
- Top-down, heel-flap construction. Toe-up knitters run the same numbers in reverse: cast on the grafting count, increase to the full.
- Counts snap to multiples of 4 for ribbing and even halves.
- The French turn’s recipe (⅔ split) suits average insteps; high insteps like a deeper gusset: pick up two extra each side.
Sock Questions, Answered
How many stitches do I cast on for a sock?
A sock casts on its foot circumference × 90% × your stitches per inch, rounded to a multiple of 4, so a 9 in foot at 8 stitches per inch casts on 64, the most common sock count. A 10 in foot at the same gauge needs 72.
How does a sock heel turn work?
A sock heel turn uses short rows across the center of the heel flap: knit to half the flap plus two stitches, ssk, k1, and turn, then slip one, purl five, p2tog, p1, and turn. Each following pass works one stitch further until all the side stitches are used, and the calculator writes your flap’s exact first rows.
When do I start the toe of a sock?
You start the toe of a sock when the foot reaches its full length minus the toe’s depth, about 1¾ in at fingering gauge. Decrease 4 stitches every other round until half remain, then every round until a third remain, and graft the toe closed.
Why do socks need negative ease?
Socks need negative ease because a sock knit at the exact foot size slides and bags as the knitting stretches. Knit about ten percent under the foot measurement so the fabric grips, or about 15% under for very stretchy ribbed socks.