Every yarn calculator — including the estimate mode on this site — starts from typical gauge: the average number of stitches per inch for a yarn weight and stitch. Real people are not average. Tension varies by a few stitches per 4 inches from person to person and even from day to day, and that alone can move the yardage by 10–15%. A swatch replaces the assumption with a measurement, which is why the swatch mode is the most accurate way to estimate yarn.
Step 1: make a big enough swatch
Use the exact yarn, needle or hook and stitch pattern you will use for the project. Cast on or chain enough stitches for at least 6 inches (15 cm) of width and work until the piece is at least 6 inches tall. A 4-inch swatch is the textbook minimum for gauge, but for weighing, a larger swatch is better: kitchen scales are typically accurate to 1 gram, and a small worsted swatch may only weigh 8–10 g, so a 1 g error becomes a 10% error in the estimate. A 6 × 6 inch worsted swatch weighs about 15–20 g; an 8 × 8 inch one around 30 g.
Work the swatch the way you will work the project. If the blanket is crocheted back and forth, work the swatch back and forth; if the hat is knitted in the round, knit the swatch in the round or use a speed swatch across the back of the needles. Include the stitch pattern itself — cables, bobbles and colorwork change yarn use dramatically.
Step 2: wash and block it
Treat the swatch the way you will treat the finished piece. Wash it, press out the water in a towel and let it dry flat, pinned if the project will be blocked. Wool relaxes and lace opens up when blocked; cotton and acrylic can grow or shrink a little. Measuring an unblocked lace swatch can overestimate yarn by 20% or more, because blocking stretches the same length of yarn over a bigger area.
Step 3: measure
Lay the dry swatch flat without stretching it. Measure the whole swatch width and height with a ruler — not a tape measure that can bend — and write both numbers down. For gauge, also count the stitches and rows in the central 4 inches, away from the edges where tension is uneven.
Compare the gauge to the pattern. If you have more stitches per 4 inches than the pattern, your fabric is denser and the project will be smaller and use more yarn per square inch; go up a needle or hook size. Fewer stitches means a looser fabric, a bigger project and less yarn per square inch; go down a size.
Step 4: weigh it (or unravel it)
Put the swatch on a kitchen or postal scale and note the weight in grams. Then read the yarn label: it gives the length and the weight of one skein, for example 200 yd (183 m) / 100 g. The yarn in the swatch is:
swatch yards = swatch grams × label yards ÷ label grams
If you do not have a scale, unravel the swatch and measure the yarn with a tape measure or a yardstick, or measure a long tail before you start and what is left afterwards. Weighing is faster and more reliable for anything bigger than a few yards.
Step 5: scale up
Divide the swatch yards by the swatch area to get your personal yarn rate, then multiply by the project area:
yards per sq in = swatch yards ÷ (swatch width × swatch height)project yards = yards per sq in × project area × overhead × (1 + extra %)
Example: a 6 × 6 inch double crochet swatch in worsted weighs 17 g. The label says 200 yd per 100 g, so the swatch contains 17 × 200 ÷ 100 = 34 yards. Its area is 36 sq in, giving 0.94 yd per sq in. A 50 × 60 inch throw is 3,000 sq in, so the fabric needs 0.94 × 3,000 = 2,830 yards; with 10% safety, 3,115 yards, or 16 skeins of 200 yards. That is noticeably more than the typical-gauge estimate — this crocheter works tighter than average, and the swatch caught it.
The swatch calculator does all of this, in inches or centimeters, yards or meters, and reports grams and skeins for your label. For garments, choose the project and size and it applies the same overhead for ribbing and seams as the estimate mode.
What overhead covers
A blanket is almost exactly its area, plus a few percent for a border. Other projects are not. Hats have ribbed brims and crown decreases; socks have reinforced heels and gussets; sweaters have ribbing, neckbands and seam allowances. The calculator multiplies the swatch rate by an overhead factor — 3% for blankets, 12% for sweaters, 15% for hats and 35% for socks — on top of the area. If your design has extra features (pockets, a hood, fringe), add them as additional safety percentage.
Common swatch mistakes
- Measuring on the needle. The fabric is compressed; take it off or at least bind off loosely.
- Not including the border. If the project has a seed-stitch or garter border, do not include it in the gauge count — but do remember to estimate it.
- Swatching in a different color. Dark and light dyes of the same yarn usually behave the same, but a different yarn "in the same weight" does not.
- Relaxed swatch, tense project. Many people knit looser when swatching and tighter on a big project. Re-measure gauge once the project is a few inches long.
A good swatch is also a sample for the washing machine test and a reference for the future. Keep it with the leftover yarn and the label; you will be glad of it when you need to repair the project years later.