I was going to figure out a pattern on my own (since I have a non-standard sized bottle) but I found this pattern with the super-easy-to-follow math to make your own custom-sized cover. Woohoo!

Gauge: 19 sts = 4” | 4.75 sts/in

CO 16 sts per needle.
Knit one round.
K12, TSK, K8, TSP, K5, TWK, K2, TSP. Knit across to second needle. Repeat. (Mental note: probably could have done with only one short row.)
Increase this round and every other round to 56 sts.
Knit body.
Decrease 6 times to 32 sts. 3 decreases at every other row, three decreases in a row.
Rib neck for… a while.
BO.
Woot!

For some reason this strikes me as ridiculously awesome. It makes me giggle.