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Yarn quantity estimator

Estimates yardage for a project of given dimensions from your own measured swatch, and converts that into balls of a specific yarn.

The question this answers: “How many balls do I need for a blanket this size, in this yarn?”

Unravel the swatch and measure it, or weigh it and scale from the ball band. Weighing is more accurate.

A 10 × 10cm swatch is 100cm². Smaller than that and the error grows fast.

Width × length of the finished piece. A 90 × 100cm baby blanket is 9,000cm².

From the ball band. Use metres, not grams — grams vary by fibre.

Covers edging, seaming and tension drift. 15% is a reasonable default; go higher for a border or colourwork.

Result

Estimated yarn needed
1863m
1620m for the fabric, plus a 15% margin.
Balls required
10 balls
At 200m per ball, leaving about 137m spare.

Worth knowing about this answer

  • Buy the whole quantity in one go, in a single dye lot. A ball bought later will very often be a visibly different shade, and on a large flat piece the join shows.
Show the working
  1. Yarn per cm²18m ÷ 100cm²0.18m/cm²
  2. Fabric requirement0.18 × 9000cm²1620m
  3. With margin1620m × 1.151863m
  4. Balls, rounded up1863m ÷ 200m10

Estimated yarn needed: 1863m. Balls required: 10 balls

How it works

Yarn per unit area from the swatch, scaled to project area, plus a stated margin, divided by metres per ball and rounded up.

What it assumes

  • Even fabric density across the project; a border or edging is additional, which is what the margin is for.
  • The swatch was worked in the yarn, hook or needles and stitch pattern the project will use.

Where it stops being reliable

  • Highly sensitive to swatch measurement accuracy; dye lots mean under-ordering is worse than over-ordering.
  • Shaped garments are not flat rectangles. Estimate the area generously or work piece by piece.

Runs entirely in your browser — nothing you type is sent anywhere. Last reviewed 2026-08-13. More on Crochet.