You have to define “average amount”. Some iceberg calving is huge, like the size of New Jersey, while some is considerably smaller. I don’t know what the ‘average’ size is. I don’t think there is one, because a lot of calving is not known or observed by people.
Second, I think the answer is infinitesimally small. Let’s say that a 200 square mile piece of iceberg split off. Let’s also assume that about 70% of the earth’s surface is ocean.
Icebergs can vary greatly in size, ranging from very large – greater than 10 million tons and hundreds of metres long – to large, medium, and small bergs. The smallest are termed “bergy bits,” which are the size of a small house, and “growlers,” which are the size of a grand piano. These smaller pieces are hazardous to ships because radar may not pick them up as they bob up and down among the waves. The average weight for a Grand Banks-area iceberg is 100,000–200,000 tons – about the size of a cubic 15-story building
Let’s also assume that oceans cover about 71 percent of the Earth’s surface, which is about 360 million square kilometers of ocean.
400000000 / 3.87500775e+15 (# pounds divided by surface area of the oceans)
equals
1.032256e-7
which is something like .0000001 feet (or about one millionth of a foot)
Bottom line – you wouldn’t notice a difference.
link to iceberg facts