Cast-On & Gauge Calculator
Turn a measured swatch into the cast-on stitches and rows you need for your target width and length.
Measure your swatch after washing and blocking it, in the actual pattern stitch, not ribbing. Add any selvedge stitches your pattern calls for on top of this count.
How it works
Gauge is almost always quoted over 4 inches, so the first step is turning that into a per-inch number: stitches per 4" divided by 4 gives stitches per inch, and the same math turns rows per 4" into rows per inch. From there, cast-on stitches is just your target width times stitches per inch, rounded to a whole stitch, and the row count for a piece is your target length times rows per inch, rounded the same way.
Worked example: your swatch measures 18 stitches and 24 rows over 4 inches. That's 4.5 stitches per inch and 6 rows per inch. For a 20 inch wide, 8 inch long panel, you cast on 90 stitches (20 × 4.5) and work 48 rows (8 × 6). Change the swatch numbers and the cast-on and row count update to match, since gauge varies by yarn, needle size, and how tightly you knit.
FAQ
Why does my gauge swatch matter so much?
Gauge is the bridge between a pattern's numbers and your actual tension. Two knitters using the same yarn and needle size can still get different stitch counts per inch, and that difference compounds over a whole sweater or blanket. A swatch tells you your real numbers before you commit hours of work to the wrong size.
Do I really need to wash and block my swatch first?
Yes, if the finished project will be washed or blocked. Many fibers relax or bloom with water, which changes the stitch count per inch, sometimes by a lot with wool or bamboo blends. Measuring an unblocked swatch can send you into a project with the wrong gauge even though the swatch looked right on the needles.
What if my gauge is close but not exact?
A small difference, a few tenths of a stitch per inch, usually just means a slightly different finished size, which may not matter for a scarf or dishcloth. For anything that needs to fit, like a sweater or hat, try a needle size up or down and swatch again rather than pushing ahead with an off gauge.
Does this work for crochet too?
Yes. Crochet gauge swatches work the same way, just measured over your foundation chain and rows of stitches instead of a knit cast-on. Swap "cast on" for "chain this many stitches" and the math is identical.
For more on the basics behind this calculator, see what gauge is and why it matters, how to cast on in knitting, and what blocking is and how to do it.