Multiply by 2...and add 1 to the total.
If it were mult of 3+1...
ETA: BTW, if you're new to the concept, and planning to add various st patts, cables, try to use ones that are equally divisible in their row counts. For ex, if your largest cable has a 12-row repeat, try to use other st patts or cables with 2-, 4- or 6-row reps. Rather than one that's 8. By using the common divisibles the 12-row rep will end at the same time as the others, making for less confusion.