Stitches per inch — the foundation of any knitting pattern. Match the pattern's gauge exactly or the garment will be the wrong size.
Gauge in knitting and crochet is the number of stitches and rows per unit length (usually per inch or per 4 inches / 10 cm) at a given tension with a given yarn and needle size. Every pattern specifies gauge and every knitter must match it to get the right final size.
Gauge is set by three things: yarn weight, needle size, and the knitter's personal tension. Two knitters using the same yarn and needle can get different gauges because one knits tighter than the other. That is why "knit a swatch and measure" is the rule.
Worsted weight
Typical gauge 20 sts / 28 rows per 4 in on US 7 (4.5 mm)
Pattern calls for 22 sts/4in; you get 24
Go up one needle size (US 8) to loosen.
Knit Gauge → Cast-On
Turn a swatch gauge into the exact cast-on and total row count for any size garment.
Yarn Yardage Estimator
Total yards and skeins for a project by type, size, and yarn weight — with a buffer recommendation.
Knit Shaping Rate
Evenly space increases or decreases across a sleeve, hem, or shoulder — "inc 1 every X rows".