I've gained a bit over half an inch in the 18 months of Penis Enlargement, but a good portion of that 18 months was strictly length training. I'd say I trained girth with wet jelqs and horse squeezes for the first three months, then did no girth for almost a year. The last few months I have picked back up on girth, doing clamping mostly, with some wet jelqs for good measure.
Overall, I'd say I gained about half of my girth in the first three month girth training period, and half of my girth in the last few months of girth training. At this rate, it is about 1" per year (but obviously some diminishing returns apply).