When looking at the pitch of your connector and the pitch of your ribbon cable you will need to understand they are often not the same. If you have a 2 row connector your ribbon cable pitch will be half of your connector mating pitch.
For example IDC socket HHKC10H-ND is a 10 position 2 row connector. This connector has a mating pitch of .100" (2.54mm) and a row spacing of .100" (2.54mm). The pitch of the cable that will mate with this connector will be .050" (1.27mm). These measurements are shown and should always be verified on the manufacturer’s data sheet.
There is also a post on Pitch of a Connector that shows how to measure your connector pitch if you have any questions.
The pitch of your ribbon cable can generally be determined by measuring from outside edge of the cable to outside edge of the cable and dividing that by the total number of conductors.