I want to adapt a pattern I have for someone with a larger head. The pattern as written says that it has an UNstretched circumference of 18 1/2"; doesn't say what it should stretch to. (It's corrugated ribbing at this point.) Gauge is 32=4"; cast-on is 136 stitches.
The head I'm knitting for is 23". The ribbing in this case won't be corrugated, if that matters.
How many stitches should I cast on? It's the unstretchedness of the original measurements that has me thrown...
I usually put ribbing at the edge of my hats and figure it this way. The circumference of the head times the stitches per inch equals the cast on. Then taking a needle 2 sizes smaller than that used for the gauge swatch work the first inch or more in ribbing. That will give you a stretchy edge to your hat. If you like it to fit snuggly, subtract 10%.