What size were the 12 baskets used to collect left-over pieces of bread when Jesus fed the 5000?

According to Mark 6:43, there were "twelve basketfuls" of leftover pieces of fish and bread gathered up after the 5,000 men (plus an undetermined number of women & children) ate. Mark 8:8 documents "seven basketfuls" of leftovers after feeding 4,000 men (again, not counting women & children).