Periwinkle and Mint Spacing

I am planning on purchasing some vinca minor and some mint speedplugs this fall for groundcover planting. How far apart should I plan on planting them? This helps me estimate how many I'll need.

Plant periwinkle (Vinca minor) 6 inches apart. You do not say which mint you are thinking about, but the small creeping varieties (e.g. corsican, carpet pennyroyal) are planted 4 to 8 inches apart; other taller varieties are planted 18 to 24 inches apart.