For an arbitrary number of columns:

```
awk -v col=6 '{printf "%s%s", (NR>1) ? (NR-1) % col ? "," : RS : "", $0}
 END{if (NR) print ""}' < your-file
```

With `pr` (assuming the input like in your sample doesn't contain one of the special sequences recognised by some `pr` implementations; with the GNU one (as found on `pr`), that includes at least the form-feed character):

 pr -t -a -s, -6 < your-file