C2C crochet calculator

Corner-to-corner (C2C) is worked diagonally in small tiles, so the usual row maths does not apply. This calculator turns a tile swatch into tiles across and down, the number of diagonal rows, the rows where you change from increasing to decreasing, and the yarn each phase uses, so you can check your progress on a kitchen scale.

How to use the calculator

1. Choose standard C2C (tiles of 3 dc) or mini C2C (tiles of 2 hdc).
2. Make a swatch of at least 5 × 5 tiles, block it, and enter the tiles and the width and height they cover.
3. Optionally weigh the swatch for the yarn amounts.
4. Enter the blanket size and your yarn label.

How the calculator works

Tile width and height are measured separately, because C2C tiles are often slightly taller than wide:

Tile width = swatch width ÷ tiles across, and the same for the height.

Tiles across = blanket width ÷ tile width; tiles down = blanket length ÷ tile height, each rounded.

Diagonal rows = tiles across + tiles down − 1

The rows fall into three phases. With S the shorter side in tiles and L the longer:

• Increase at both edges until the row reaches the shorter side: S × (S + 1) ÷ 2 tiles.
• Increase at one edge and decrease at the other (rectangles only) until you reach the longer side: (L − S) × S tiles.
• Decrease at both edges to the final corner: (S − 1) × S ÷ 2 tiles.

With a weighed swatch, each tile uses the swatch weight ÷ the swatch's tiles, and the total yarn has 10% extra added.

Reading your results

• Tiles across × down, tiles in total and diagonal rows.
• Finished size after rounding to whole tiles.
• Yarn with 10% extra: in both units, with balls and grams.
• The three phases: the rows in each phase, its tiles, and the yarn you should have used by the end of it (without the 10% extra), to weigh against.
• How each row starts: the start of the first row, the increase rows and the decrease rows for your tile type.

Worked example

A 5 × 5 tile swatch measures 3.75 × 3.75 in, 0.75 in per tile, and weighs 7.5 g (0.3 g per tile). You want a 45 × 60 in throw in 220 yd per 100 g yarn.

• Tiles: 45 ÷ 0.75 = 60 across and 60 ÷ 0.75 = 80 down; 4,800 tiles.
• Diagonal rows: 60 + 80 − 1 = 139.
• Rows 1 to 60 increase at both edges (1,830 tiles). Rows 61 to 80 increase at one edge and decrease at the other (1,200 tiles). Rows 81 to 139 decrease at both edges (1,770 tiles).
• By the end of each phase you should have used about 549 g, 909 g and 1,440 g.
• Yarn: 3,485 yd (3,187 m) with 10% extra, 16 balls.

US and UK terms

Standard C2C tiles are ch 3 and 3 dc in US terms (3 tr in UK terms); mini C2C uses 2 hdc (2 htr in UK terms). Switch the terms toggle to see the row instructions in UK terms.

Accuracy and limits

• The tile counts and phases are exact, and covered by our automated tests. The yarn depends on your swatch.
• Every tile is counted as using the same yarn; the slip stitches at the edges are not counted separately, which the 10% extra covers.
• Changing colours for a picture uses more yarn in ends and bobbins than one colour.

Common mistakes

1. Measuring one tile. Measure several tiles across the middle of a blocked swatch and let the calculator divide.
2. Turning too early on a rectangle. Keep increasing on one edge until the longer side is complete; only the shorter side starts decreasing first.
3. Using an unblocked swatch. C2C tiles relax when blocked, often more in height.

Tips for more accurate results

• Weigh what you have used at each phase change to check you are on track.
• For a picture blanket, plan the graph at the tile counts shown here; the filet and tapestry chart calculator helps with other chart-based work.
• Work out how much yarn you can spare for a border with the border yarn calculator.

Frequently asked questions