Crochet border yarn calculator

A border looks small but covers a lot of fabric: 3 in around a throw can be a quarter as big as the blanket itself. This calculator works out the border's area, including the corners, and the yarn and balls it needs for a flat, shell or ruffled edging, so you do not run out on the last side.

How to use the calculator

1. Enter the blanket size before the border, and the border width on each side.
2. Choose the style: flat, shell or scallop, soft ruffle or full ruffle.
3. Enter the yarn per area from a weighed swatch, or a rate you already know.
4. Enter your ball length and the extra to allow.

How the calculator works

The border is four strips along the sides plus four squares at the corners:

Border area = 2 × border width × (blanket width + blanket length) + 4 × border width²

The corner squares are the part simple perimeter sums leave out.

Border yarn = area × yarn per area × style multiplier × (1 + extra)

From a swatch, the yarn per area is the swatch weight ÷ its area × the length per gram of your yarn. The style multipliers are rules of thumb: 1 for a flat border, 1.3 for shells or scallops, 2 for a soft ruffle (2 stitches in each stitch) and 3 for a full ruffle (3 in each).

Reading your results

• Border area: and its share of the blanket's area. A warning appears if the border is more than 60% of the blanket.
• Border yarn: in both units, including your extra.
• Balls for the border: rounded up.

Worked example

A 3 in flat border around a 46 × 56 in throw:

• Area: 2 × 3 × (46 + 56) + 4 × 3² = 612 + 36 = 648 sq in, 25% of the blanket's area.
• Yarn: at 1.1 yd per sq in with 10% extra, 648 × 1.1 × 1.1 = 784 yd (717 m).
• Balls: 4 balls of 220 yd.

Accuracy and limits

• The arithmetic is exact and covered by our automated tests; the result is an estimate, because border stitches and your yarn per area vary.
• The style multipliers are rules of thumb. Work one round and weigh it to check, especially for ruffles.
• The default known rate (1.1 yd per sq in) is only an example; enter your own, or use a weighed swatch.

Common mistakes

1. Forgetting the corners. On a wide border, the four corner squares add a noticeable amount.
2. Using the blanket's finished size. Enter the size before the border; the border width is added around it.
3. Treating a ruffle like a flat border. A ruffle can use two or three times as much yarn.

Tips for more accurate results

• Work one round of the border, weigh the yarn used, and multiply by the number of rounds.
• Buy the border yarn with the blanket yarn, from the same dye lot.
• Plan the border's stitches with the border stitch calculator.

Frequently asked questions