Whether you are crocheting a round coaster, a mandala rug, a beret crown, or the base of a market tote, working in the round is a core crochet skill. Yet almost every crocheter encounters two infuriating distortions: the work curls upward into a bowl (cupping), or the edges ripple into wavy lettuce ruffles (ruffling).
These problems are not matters of bad luck; they are purely geometric. In Euclidean geometry, the circumference of a circle is calculated as C = 2Οr. Because each round of crochet stitches increases the radius (r) of the circle by the exact height of the stitch, the circumference must expand by a constant number of stitches on every single round to remain completely flat.
The Geometry of a Flat Circle
The infographic below illustrates the three circle states and the exact increase rates required for each stitch family:
Standard Increase Rules by Stitch Height
Because taller stitches create a wider radius jump per round, taller stitches require a larger starting ring and more increases per round:
| Stitch Type (US) | Starting Magic Ring (Rnd 1) | Increases per Round | Round 2 Stitches | Round 3 Stitches | Round 4 Stitches |
|---|---|---|---|---|---|
| Single Crochet (sc) | 6 stitches (or 7β8 for stiff yarns) | +6 sts/round | 12 sts (2 sc in each) | 18 sts (1 sc, inc) | 24 sts (2 sc, inc) |
| Half Double Crochet (hdc) | 8 to 9 stitches | +8 to 9 sts/round | 16β18 sts (2 hdc in each) | 24β27 sts (1 hdc, inc) | 32β36 sts (2 hdc, inc) |
| Double Crochet (dc) | 12 stitches | +12 sts/round | 24 sts (2 dc in each) | 36 sts (1 dc, inc) | 48 sts (2 dc, inc) |
| Treble Crochet (tr) | 16 to 18 stitches | +16 to 18 sts/round | 32β36 sts (2 tr in each) | 48β54 sts (1 tr, inc) | 64β72 sts (2 tr, inc) |
How to Stop Your Circle from Turning into a Hexagon
If you follow a standard pattern where the increase always happens at the start of a repeat (e.g., [2 sc, inc] around, followed by [3 sc, inc] around), all of your increases stack directly above each other. That extra bulk pushes outward in straight lines, turning your smooth circle into a 6-sided hexagon or 12-sided polygon.
To keep the circle circular, stagger your increases on even rounds:
- Odd Rounds (1, 3, 5): Work normallyβe.g., Round 3 is
[1 sc, inc] around; Round 5 is[3 sc, inc] around. - Even Rounds (2, 4, 6): Split the plain stitches in half before the first increase. For example, on Round 4 (where the repeat is 2 plain stitches and 1 increase), work:
1 sc, inc, [2 sc, inc] around to last stitch, 1 sc. This offsets the increases into the valleys between previous increases, resulting in a perfect circular curve.
For custom diameter, stitch count, and circumference calculations across any hook and yarn combination, use our Flat Circle Calculator.