I don't want to waste space since I don't have a lot, but I don't want to get smaller bulbs either. At the farm there is at least a foot between rows, maybe 18 ", and plants are spaced about 8 inches apart. I got some big bulbs the year I used 8 inch spacing and a foot between rows, but then it was a good year for garlic anyway.
Last year I tightened up and bulbs were not as big - but it was a really cold year and nobody had really big bulbs this time around.
Omafra says 12 cm (5 inches) minimum spacing in row for porcelains, 7 cm (3 inches?) for smaller bulbed varieties, and a minimum of 20 cm (8 inches) between rows. My dibbler is about an inch so I put 5 inches between holes for the porcelains I just planted today, and 8 inch between rows like last year.
Elsewhere I read that tighter spacing can produce great garlic but requires rich soil, weed control and moisture management. I think my soil is good, and I keep em weeded by hand, but I rarely water so that may be the key issue.
What spacing do you use in your garden or farm, and why does it work best for you?